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Sample records for bouguer gravity anomalies

  1. Complete Bouguer gravity anomaly map of the state of Colorado

    USGS Publications Warehouse

    Abrams, Gerda A.

    1993-01-01

    The Bouguer gravity anomaly map is part of a folio of maps of Colorado cosponsored by the National Mineral Resources Assessment Program (NAMRAP) and the National Geologic Mapping Program (COGEOMAP) and was produced to assist in studies of the mineral resource potential and tectonic setting of the State. Previous compilations of about 12,000 gravity stations by Behrendt and Bajwa (1974a,b) are updated by this map. The data was reduced at a 2.67 g/cm3 and the grid contoured at 3 mGal intervals. This map will aid in the mineral resource assessment by indicating buried intrusive complexes, volcanic fields, major faults and shear zones, and sedimentary basins; helping to identify concealed geologic units; and identifying localities that might be hydrothermically altered or mineralized.

  2. Optimization schemes for the inversion of Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, Azucena

    associated with structural changes [16]; therefore, it complements those geophysical methods with the same depth resolution that sample a different physical property (e.g. electromagnetic surveys sampling electric conductivity) or even those with different depth resolution sampling an alternative physical property (e.g. large scale seismic reflection surveys imaging the crust and top upper mantle using seismic velocity fields). In order to improve the resolution of Bouguer gravity anomalies, and reduce their ambiguity and uncertainty for the modeling of the shallow crust, we propose the implementation of primal-dual interior point methods for the optimization of density structure models through the introduction of physical constraints for transitional areas obtained from previously acquired geophysical data sets. This dissertation presents in Chapter 2 an initial forward model implementation for the calculation of Bouguer gravity anomalies in the Porphyry Copper-Molybdenum (Cu-Mo) Copper Flat Mine region located in Sierra County, New Mexico. In Chapter 3, we present a constrained optimization framework (using interior-point methods) for the inversion of 2-D models of Earth structures delineating density contrasts of anomalous bodies in uniform regions and/or boundaries between layers in layered environments. We implement the proposed algorithm using three different synthetic gravitational data sets with varying complexity. Specifically, we improve the 2-dimensional density structure models by getting rid of unacceptable solutions (geologically unfeasible models or those not satisfying the required constraints) given the reduction of the solution space. Chapter 4 shows the results from the implementation of our algorithm for the inversion of gravitational data obtained from the area surrounding the Porphyry Cu-Mo Cooper Flat Mine in Sierra County, NM. Information obtained from previous induced polarization surveys and core samples served as physical constraints for the

  3. World Gravity Map: a set of global complete spherical Bouguer and isostatic anomaly maps and grids

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Kuhn, M.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2012-04-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. The Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, 2011). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy-Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial

  4. A simple Bouguer gravity anomaly map of southwestern Saudi Arabia and an initial interpretation

    USGS Publications Warehouse

    Gettings, M.E.

    1983-01-01

    Approximately 2,200 gravity stations on a 10-km2 grid were used to construct a simple Bouguer gravity anomaly map at 1:2,000,000 scale along a 150-km-wide by 850-km-long strip of the Arabian Peninsula from Sanam, southwest of Ar Riyad, through the Farasan Islands and including offshore islands, the coastal plain, and the Hijaz-Asir escarpment from Jiddah to the Yemen border. On the Precambrian Arabian Shield, local positive gravity anomalies are associated with greenstone belts, gneiss domes, and the Najd fault zones. Local negative gravity anomalies correlate with granitic plutonic rocks. A steep gravity gradient of as much as 4 mgal-km-1 marks the continental margin on the coastal plain near the southwestern end of the strip. Bouguer gravity anomaly values range from -10 to +40 mgal southwest of this gradient and from -170 to -100 mgal in a 300-km-wide gravity minimum northeast of the gradient. Farther northeast, the minimum is terminated by a regional gradient of about 0.1 mgal-km-1 that increases toward the Arabian Gulf. The regional gravity anomaly pattern has been modeled by using seismic refraction and Raleigh wave studies, heat-flow measurements, and isostatic considerations as constraints. The model is consistent with the hypothesis of upwelling of hot mantle material beneath the Red Sea and lateral mantle flow beneath the Arabian plate. The model yields best-fitting average crustal densities of 2.80 g-cm-3 (0-20 km depth) and 3.00 g-cm-3 (20-40 km depth) southwest of the Nabitah suture zone and 2.74 g-cm-3 (0-20 km depth) and 2.94 g-cm-3 (20-40 km depth) northeast of the suture zone. The gravity model requires that the crust be about 20 km thick at the continental margin and that the lower crust between the margin and Bishah (lat 20? N., long 42.5? E.) be somewhat denser than the lower crust to the northeast. Detailed correlations between 1:250,000- and 1:500,000-scale geologic maps and the gravity anomaly map suggest that the greenstone belts associated

  5. Principal facts and a discussion of terrain correction methods for the complete Bouguer gravity anomaly map of the Cascade Mountains, Washington

    SciTech Connect

    Danes, Z.F.; Phillips, W.M.

    1983-02-01

    Since 1974, the Division of Geology and Earth Resources, in conjunction with the US Department of Energy, has supported gravity studies in the Cascade Mountains of Washington State. Results of the Cascade gravity project are summarized graphically as a complete Bouguer gravity anomaly map of the Cascade Mountains, Washington (Danes and Phillips, 1983). This report provides supplementary data and documentation for the complete Bouguer gravity anomaly map. Presented are principal gravity facts, simple Bouguer and Free-air gravity anomalies, computational methods, error analysis and a discussion of terrain corrections.

  6. Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

    USGS Publications Warehouse

    Plouff, Donald

    1992-01-01

    A residual isostatic gravity map (sheet 2) was prepared so that the regional effect of isostatic compensation present on the Bouguer gravity anomaly map (sheet 1) would be minimized. Isostatic corrections based on the Airy-Heiskanen system (Heiskanen and Vening Meinesz, 1958, p. 135-137) were estimated by using 3-minute topographic digitization and applying the method of Jachens and Roberts (1981). Parameters selected for the isostatic model were 25 km for the normal crustal thickness at sea level, 2.67 g/cm3 for the density of the crust, and 0.4 g/cm3 for the contrast in density between the crust and the upper mantle. These parameters were selected so that the isostatic residual gravity map would be consistent with isostatic residual gravity maps of the adjacent Walker Lake quadrangle (Plouff, 1987) and the state of Nevada (Saltus, 1988c).

  7. Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

    2006-12-01

    Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys

  8. Principal Facts and a Discussion of Terrain Correction Methods for the Complete Bouguer Gravity Anomaly Map of the Cascade Mountains, Washington

    SciTech Connect

    Danes, Z.F.; Phillips, William M.

    1983-02-01

    Since 1974, the Division of Geology and Earth Resources, in conjunction with the US Department of Energy, has supported gravity studies in the Cascade Mountains of Washington State (Danes, 1975, 1979, 1981; Korosec and others, 1981). The purpose of the work has been to gather baseline gravity data for eventual contribution to geothermal resource evaluation. However, it is expected that the Cascade gravity data will prove useful in a number of future endeavors such as fossil fuel and mineral exploration, as the gravity method is a basic tool of the exploration geophysicist. Results of the Cascade gravity project are summarized graphically as a complete Bouguer gravity anomaly map of the Cascade Mountains, Washington. This report provides supplementary data and documentation for the complete Bouguer gravity anomaly map. Presented are principal gravity facts, simple Bouguer and Free-air gravity anomalies, computational methods, error analysis and a discussion of terrain corrections. It is hoped that release of this report will encourage analysis of Cascade gravity data beyond the standard treatment (complete Bouguer gravity anomaly at a reduction density of 2.67 g/cm{sup 2}) presented in Danes and Phillips, (1983).

  9. A new Bouguer gravity anomaly field for the Adriatic Sea and its application for the study of the crustal and upper mantle structure

    NASA Astrophysics Data System (ADS)

    Tassis, G. A.; Grigoriadis, V. N.; Tziavos, I. N.; Tsokas, G. N.; Papazachos, C. B.; Vasiljević, I.

    2013-05-01

    The purpose of this paper is the development of a new Bouguer anomaly map for the broader Adriatic Sea area to be used as geo-scientific tool which will answer questions mainly regarding the deep and intermediate depth structure of the Adriatic and its surrounding areas. As a first step, a consistent, high-resolution and accuracy free-air gravity anomaly database is created using all the available terrestrial and satellite altimetry data sources. The least-squares collocation (LSC) method is employed to validate the different gravity data sets through an appropriate covariance analysis and following the remove-compute-restore procedure (RCR) for the detailed study of the gravity spectrum. The finally generated gravity database has a resolution of a 0.0333° (˜3.2 km) in both latitude and longitude, while its external and internal accuracy is estimated to about ±5 mGal and ±0.5 mGal, respectively. Based on the derived free-air gravity database a new Bouguer gravity anomaly database is determined at the same resolution for the wider region of the Adriatic Sea. Comparison with existing results confirms the reliability of the new Bouguer map for the study area, mainly due to the combination of both land and sea data. The derived Bouguer anomaly map can support different kind of geophysical investigations of both local and regional structure of the study region. As an example three density models are constructed along selected cross sections extracted from the Bouguer anomaly database, in order to obtain structural information for the crustal-upper mantle structure of the region and draw relevant conclusions. The obtained results show that the Bouguer map can provide important information for the lower-crustal/upper-mantle depth range but also helps to constrain the 2D geometry of the shallow geological units, in very good agreement with the observed surface geology and the current understanding of the geotectonic setting of the area.

  10. GTeC-A versatile MATLAB® tool for a detailed computation of the terrain correction and Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Cella, Federico

    2015-11-01

    Gravity Terrain Correction (GTeC) is a versatile MATLAB® code for terrain correction aimed to this purpose and capable of going beyond the limits of other public domain codes targeted to this aim. It runs with input gravity data (absolute measurements or free air anomalies) at the land/sea surface and with one or more DTMs (indifferently gridded or scattered) at different detail levels. Each of them can be used to calculate the gravity contribution of a concentric terrain zone around the point station with increasing resolution toward the center. The user can choose between two alternative algorithms for terrain modeling. The simplest one considers each grid point as the flat top of a squared prism. For areas closer to the point station a second algorithm can be chosen to better approximate the relief, with respect to others formulas, by means of a tessellation based network formed by triangular prisms. A more precise terrain correction is therefore achieved, especially in presence of high topographic gradients or just outside the sea/land boundaries. In the last case a suitable algorithm was expressly devised to fit the tessellation based network to the irregular trend of the coastline. GTeC calculates also free air anomalies and both plate and curvature corrections, providing also a complete graphic output including topography, free air anomalies, plate correction, total terrain correction, Bouguer anomalies and the terrain effect due to each computational zone. GTeC speeds up CPU times taking advantage from the parallel computing functions and from the vectorization code, both exploited in MATLAB®. Two code versions of GTeC (for normal or parallel computation), executable under MATLAB environment (pcode), are fully available as public domain software. The results of a synthetic case, of a real case at the regional scale and of a microgravity survey carried out at a short scale, are here presented.

  11. Bouguer gravity anomaly map of the Twentynine Palms Marine Corps Base and vicinity, California

    USGS Publications Warehouse

    Moyle, W.R., Jr.

    1984-01-01

    A gravity study of the Twentynine Palms Marine Corps Base and vicinity, California, based on 495 gravity measurements, has been completed. The resulting contour map of the area shows that the ground-water basin ranges in depth from less than a foot at the edges of the basin to about 10,500 feet at the center of a gravity low near Deadman Lake. This study will aid in later studies to determine quantities of water in storage beneath the Marine Corps Base. (USGS)

  12. On the Optimization of the Inverse Problem for Bouguer Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, A.; Velasco, A. A.; Gutierrez, A. E.

    2013-12-01

    Inverse modeling of gravity data presents a very ill-posed mathematical problem, given that solutions are non-unique and small changes in parameters (position and density contrast of an anomalous body) can highly impact the resulting Earth's model. Although implementing 2- and 3-Dimensional gravitational inverse problems can determine the structural composition of the Earth, traditional inverse modeling approaches can be very unstable. A model of the shallow substructure is based on the density contrasts of anomalous bodies -with different densities with respect to a uniform region- or the boundaries between layers in a layered environment. We implement an interior-point method constrained optimization technique to improve the 2-D model of the Earth's structure through the use of known density constraints for transitional areas obtained from previous geological observations (e.g. core samples, seismic surveys, etc.). The proposed technique is applied to both synthetic data and gravitational data previously obtained from the Rio Grande Rift and the Cooper Flat Mine region located in Sierra County, New Mexico. We find improvements on the models obtained from this optimization scheme given that getting rid of geologically unacceptable models that would otherwise meet the required geophysical properties reduces the solution space.

  13. Worldwide complete spherical Bouguer and isostatic anomaly maps

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2011-12-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free air and Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, submitted). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis

  14. Aeromagnetic and complete Bouguer gravity anomaly maps of the Hunter-Fryingpan Wilderness area, Pitkin County, Colorado

    USGS Publications Warehouse

    Campbell, D.L.

    1981-01-01

    Behrendt and others (1968) pointed out the close correlation between a belt of extreme gravity lows (Behrendt and Bajwa, 1974) and a zone of precious and base mineral deposits (Tweto and Simms, 1963, fig. 1).  Tweto and Case (1972) showed that this belt of gravity lows probably reflects a series of Laramide and post-Laramide intrusions of relatively low density which may have influenced the hydrothermal systems responsible for much of the mineralization in the Colorado Mineral Belt.

  15. Bouguer Anomaly of the Solfatara Hydrothermal Plume, Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Young, N. K.; Gottsmann, J.

    2015-12-01

    Solfatara tuff cone is the most hydrothermally active area within Campi Flegrei caldera, a resurgent nested caldera near Naples, Italy. Hydrothermal gases and fluids are released most vigorously here and at Pisciarelli nearby. Models explaining the measured fumarole emissions and deformation require a plume of ascending hot water vapour and CO2 from depth. Here we present preliminary findings from a new gravity survey which aims at i) creating a high precision Bouguer anomaly map of Solfatara and ii) imaging the hydrothermal plume. We carried out a high spatial density gravity survey of Solfatara and the surrounding area using a Scintrex CG5 gravimeter and simultaneous benchmark localisation using a GNSS system. We created a dense grid of 51 stations within Solfatara crater, and a reduced density network of 37 further stations outside the crater to 3km distance. Other geophysical techniques such as electromagnetism, electrical resistivity, and active seismic imaging have resolved the subsurface architecture to depths between a few hundred meters to 3km depth. Our coverage and spacing should capture the details of the plume under Solfatara and have resolution to approximately 3km depth.

  16. Local gravity anomalies produced by dislocation sources.

    USGS Publications Warehouse

    Savage, J.C.

    1984-01-01

    Dilatancy, in general, does not correspond to the absence of a free air anomaly, as might be suggested by the special case of a spherical source of dilatation. For two-dimensional models a cylindrical source of dilatation produces no free air gravity anomaly, dip-slip faulting produces no Bouguer anomaly, and open cracks produce a Bouguer anomaly equal to that which would be produced had the material within the crack been mined out without deforming the solid. -from Author

  17. An updated Bouguer anomaly map of south-central West Africa

    USGS Publications Warehouse

    Hastings, David A.

    1983-01-01

    A new Bouguer gravity anomaly map compiled for western Africa adds data for Ghana, Guinea, and Liberia.The new data add detail to a key part of the Eburnean shield and assist in the development of a model of rifting at the time of the Eburnean orogeny, 2000 million years ago. This model includes a framework for the deposition of the region's mineral deposits. The model and existing field data can be used to guide future minerals exploration in the region.

  18. New free-air and Bouguer gravity fields of Taiwan from multiple platforms and sensors

    NASA Astrophysics Data System (ADS)

    Hwang, Cheinway; Hsu, Hung-Jui; Chang, Emmy T. Y.; Featherstone, W. E.; Tenzer, Robert; Lien, Tzuyi; Hsiao, Yu-Shen; Shih, Hsuan-Chang; Jai, Pang-Ho

    2014-01-01

    We construct 1‧ × 1‧ grids of free-air and Bouguer gravity anomalies around Taiwan with well-defined error estimates for quality assessment. The grids are compiled from land, airborne and shipborne gravity measurements, augmented with altimeter gravity at sea. Three sets of relative land gravity measurements are network-adjusted and outlier-edited, yielding accuracies of 0.03-0.09 mGal. Three airborne gravity sets are collected at altitudes 5156 and 1620 m with accuracies of 2.57-2.79 mGal. Seven offshore shipborne gravity campaigns around Taiwan and its offshore islands yield shallow-water gravity values with 0.88-2.35 mGal accuracies. All data points are registered with GPS-derived geodetic coordinates at cm-dm accuracies, allowing for precise gravity reductions and computing gravity disturbances. The various datasets are combined by the band-limited least-squares collocation in a one-step procedure. In the eastern mountainous (or offshore) region, Bouguer anomalies and density contrasts without considering the oceanic (or land) topographic contribution are underestimated. The new grids show unprecedented tectonic features that can revise earlier results, and can be used in a broad range of applications.

  19. Seismic b-Values, Bouguer Gravity and Heat Flow Data Beneath Eastern Anatolia, Turkey: Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Maden, Nafiz; Öztürk, Serkan

    2015-07-01

    In this paper, we analyze the relationships between the seismic b-values, Bouguer gravity and heat flow data in the Eastern Anatolia region of Turkey. For this purpose, spatial distributions of b-value, Bouguer gravity and heat flow have been presented for different depths and locations. In distinction to previous studies which have used only two parameters (gravity and seismic b-value or heat flow and seismic b-value), we have combined seismic b-values, Bouguer gravity and heat flow data to determine the new results on the active tectonics of the Eastern Anatolia region. Our analysis shows that there are significant and robust correlations amidst the heat flow data, Bouguer gravity anomaly and seismic b-values. The crustal structure is thick in areas where the large negative gravity anomalies and low b-values are observed. On the contrary, the regions with positive gravity anomalies and high b-values are likely to be associated with magma chambers or crustal low-velocity zones. We also provide some evidence suggesting that high b-values and high heat flow values can be related to the magmatic activities beneath the volcanic chain in the Eastern Pontide orogenic belt. Consequently, we have reached some conclusions for the Eastern Anatolia region: (1) The Moho to surface is rather thick and earthquakes are relatively smaller beneath the volcanic chain where the high heat flow values are observed, (2) a southward subduction model could have existed for the development of the Pontides during the late Mesozoic-Cenozoic era, (3) hot and unstable mantle lid zones or a lithosphere deprived of mantle under the study region is much more plausible, (4) a southward movement of the subduction plate and a northward extension of the Black Sea increase the state of stress along the trench axis and decrease the b-value, and (5) these movements may load the stress energy to the fault zones, thereby causing the catastrophic earthquakes in the Eastern Anatolia region.

  20. Fractal Characteristics of Geomorphology Units as Bouguer Anomaly Manifestations in Bumiayu, Central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Agus Nur, Andi; Syafri, Ildrem; Muslim, Dicky; Hirnawan, Febri; Raditya, Pradnya P.; Sulastri, Murni; Abdulah, Fikri

    2016-01-01

    Bumiayu in Central Java, Indonesia, has a typical landform characteristics. Differences of topography on each geomorphological unit indicated by the value of fractal dimension. This research provides important information on the influence of geomorphology conditions and subsurface geological phenomenon of research area based on fractal application. This research methodology relies on laboratory analysis and field observation. Landform is a characteristics of Bouguer anomaly contour manifestation. It is indicated by occurences of significant correlation between the Bouguer anomaly countour and geological cross section as well topography contour slope and Bouguer anomaly contour slope. Based on spatial analysis, morphology of research area is dominated by very high steep hills (more than 60%). Result of Bouguer anomaly countour analysis also shows that research area dominated by very high steep hills (more than 55%). Statistical analysis between the fractal value of lineament in Digital Elevation Model and fractal value of lineament in Bouguer anomaly countour as well the fractal value of topography countour and fractal value of Bouguer anomaly countour shows that the relationship was not significant. Further, the entire result of this verified research shows clearly that geomorphology conditions represents subsurface geological phenomenon.

  1. On Gravity Inversion by No-Topography and Rigorous Isostatic Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Sjöberg, Lars E.; Bagherbandi, Mohammad; Tenzer, Robert

    2015-10-01

    We discuss some theoretical aspects and practical consequences of using traditional versus "new"/rigorous formulations of the Bouguer and isostatic gravity anomalies/disturbances. In principle, the differences between these two concepts are in the definition of the so-called secondary indirect topographic effect (SITE) on the gravity data. Although we follow the tradition to call this effect SITE, we show that it is formally a direct topographic effect (DITE), needed to remove all topographic signal, but in practice not regarded as such. Consequently, there is a need for a no- topography gravity anomaly, which removes all topographic effects, leaving the below-crust Earth transparent for gravity inversion. Similarly, a rigorous isostatic gravity anomaly includes also a compensation effect for the SITE. By using a simple topographic model, we confirm a theoretically found ratio of 2/( n + 1) between the magnitudes of the SITE and DITE by wavelength (spherical harmonic degree n), both for the Bouguer and isostatic gravity anomalies. Finally, global gravity inversions are applied by utilizing the Vening Meinesz-Moritz isostatic model to determine the Moho geometry using the Bouguer gravity disturbances/anomalies and the no-topography gravity anomalies, and the results are compared. The numerical results confirm our theoretical findings that the Bouguer gravity disturbances and the no-topography gravity anomalies provide very similar results. A comparison of these gravimetrically computed Moho depths with the CRUST1.0 seismic model shows rms agreements of 4.3 and 4.5 km, respectively. This is a significant improvement when compared to the Moho result obtained by using the Bouguer gravity anomalies, yielding the rms difference of 7.3 km for the CRUST1.0 model. These results confirm a theoretical deficiency of the classical definition of the Bouguer and isostatic gravity anomalies, which do not take into consideration the SITE effects on the topography and its

  2. Eastern US crustal thickness estimates from spectral analysis and inversion of onshore Bouguer gravity anaomalies

    NASA Astrophysics Data System (ADS)

    Dybus, W.; Benoit, M. H.; Ebinger, C. J.

    2011-12-01

    The crustal thickness beneath much of the eastern half of the US is largely unconstrained. Though there have been several controlled source seismic surveys of the region, many of these studies suffer from rays that turn in the crust above the Moho, resulting in somewhat ambiguous crustal thickness values. Furthermore, the broadband seismic station coverage east of the Mississippi has been limited, and most of the region remains largely understudied. In this study, we estimated the depth to the Moho using both spectral analysis and inversion of Bouguer gravity anomalies. We systematically estimated depths to lithospheric density contrasts from radial power spectra of Bouguer gravity within 100 km X 100 km windows eastward from the Mississippi River to the Atlantic Coast, and northward from North Carolina to Maine. The slopes and slope breaks in the radial power spectra were computed using an automated algorithm. The slope values for each window were visually inspected and then used to estimate the depth to the Moho and other lithospheric density contrasts beneath each windowed region. Additionally, we performed a standard Oldenburg-Parker inversion for lithospheric density contrasts using various reference depths and density contrasts that are realistic for the different physiographic provinces in the Eastern US. Our preliminary results suggest that the gravity-derived Moho depths are similar to those found using seismic data, and that the crust is relatively thinner (~28-33 km) than expected in beneath the Piedmont region (~35-40 km). Given the relative paucity of seismic data in the eastern US, analysis of onshore gravity data is a valuable tool for interpolating between seismic stations.

  3. Imaging subsurface density distribution beneath Montserrat (West Indies) from Bouguer gravity data

    NASA Astrophysics Data System (ADS)

    Hautmann, S.; Camacho, A. G.; Gottsmann, J.; Odbert, H. M.; Syers, T.

    2012-12-01

    High resolution static gravity data allow to resolve for spatial inhomogeneities in the Earth's gravity field by providing information on the density distribution in the shallow subsurface. Images of the subsurface density distribution and identification of structural discontinuities in the ground are of particular interest in active volcanic regions, as they bear implications for fluid migration, edifice stability and the subsurface transmission of volcanically induced stresses. Although the persistently active Soufrière Hills Volcano (SHV; Montserrat, West Indies) is currently one of the most extensively studied actively erupting stratovolcanos, a local Bouguer anomaly map of the volcano and the island of Montserrat is missing to date. In June/July 2012 we conducted a static gravity survey on Montserrat. Using a Scintrex CG-5 Autograv a total of 160 new gravity data were collected on the entire island. Site positions and elevations were obtained via a TOPCON Hiperpro dual frequency GNSS receiver/antenna. Our Bouguer gravity network provides a dense coverage (distance of 200 m between adjacent sites) of the accessible regions of the older volcanic complexes Silver Hills and Centre Hills, while (due to operator's safety) the network coverage around the active SHV is more sparse with about 1 km distance between adjacent sites. The recorded gravity data were corrected for Solid Earth Tides and ocean loading and reduced for the effect of benchmark elevation (free-air effect) and latitude. The correction for topographic effects was done via an automated algorithm based on a digital elevation model and bathymetric data. In order to model our data we performed a non-linear inversion using the inversion package GROWTH 2.0. The inversion is based on a 3-D aggregation of M parallelepiped cells, which are filled, in a growth process, by means of prescribed positive and/or negative density contrasts. This methodology provides, via an automatic approach, a free 3-D geometry

  4. Band-limited Bouguer gravity identifies new basins on the Moon

    NASA Astrophysics Data System (ADS)

    Featherstone, W. E.; Hirt, C.; Kuhn, M.

    2013-06-01

    Spectral domain forward modeling is used to generate topography-implied gravity for the Moon using data from the Lunar Orbiter Laser Altimeter instrument operated on board the Lunar Reconnaissance Orbiter mission. This is subtracted from Selenological and Engineering Explorer (SELENE)-derived gravity to generate band-limited Bouguer gravity maps of the Moon so as to enhance the gravitational signatures of anomalous mass densities nearer the surface. This procedure adds evidence that two previously postulated basins on the lunar farside, Fitzgerald-Jackson (25°N, 191°E) and to the east of Debye (50°N, 180°E), are indeed real. When applied over the entire lunar surface, band-limited Bouguer gravity reveals the locations of 280 candidate basins that have not been identified when using full-spectrum gravity or topography alone, showing the approach to be of utility. Of the 280 basins, 66 are classified as distinct from their band-limited Bouguer gravity and topographic signatures, making them worthy of further investigation.

  5. Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

    NASA Astrophysics Data System (ADS)

    Wu, Guiju; Shen, Chongyang; Tan, Hongbo; Yang, Guangliang

    2016-08-01

    This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly (G h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault (F1) or the southeast boundary of Alxa block is in accord with the western change belt of G h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault (F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.

  6. Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian platform in Syria

    SciTech Connect

    Best, J.A.; Barazangi, M. ); Al-Saad, D.; Sawaf, T.; Gebran, A. )

    1990-12-01

    This study examines the crustal structure of the Palmyrides and the northern Arabian platform in Syria by two- and three-dimensional modeling of the Bouguer gravity anomalies. Results of the gravity modeling indicate that (1) western Syria is composed of at least two different crustal blocks, (2) the southern crustal block is penetrated by a series of crustal-scale, high-density intrusive complexes, and (3) short-wavelength gravity anomalies in the southwest part of the mountain belt are clearly related to basement structure. The crustal thickness in Syria, as modeled on the gravity profiles, is approximately 40{plus minus}4 km, which is similar to crustal thicknesses interpreted from refraction data in Jordan and Saudi Arabia. The different crustal blocks and large-scale mafic intrusions are best explained, though not uniquely, by Proterozoic convergence and suturing and early Paleozoic rifting, as interpreted in the exposed rocks of the Arabian shield. These two processes, combined with documented Mesozoic rifting and Cenozoic transpression, compose the crustal evolution of the northern Arabian platform beneath Syria.

  7. Detection of Lineaments in Denizli Basin of Western Anatolia Region Using Bouguer Gravity Data

    NASA Astrophysics Data System (ADS)

    Altinoğlu, Figen F.; Sari, Murat; Aydin, Ali

    2015-02-01

    The aim of this study is to investigate the geostructural boundaries of the eastern part of Western Anatolia. To achieve this, three methods, horizontal gradient, analytic signal, and tilt angle, were used. With the application of each method to the Bouguer gravity data, the common lineaments were determined using maximum values of the horizontal gradient, analytic signal maps, and zero contours of the tilt angle maps. The basement topography was also produced using the Parker-Oldenburg algorithm. Then, the produced lineaments were compared with the active fault map of the region. The results suggested that although a good agreement between the current work and earlier work exists, the new four lineament regions were also detected. We concluded that this work will lead to better understanding of Anatolian geostructural and its impact on the larger scale geological processes.

  8. Study of Southern Tyrrhenian and Sicilian regions by a sequential procedure to integrate WAM seismic tomographies and Bouguer anomaly data

    NASA Astrophysics Data System (ADS)

    Panepinto, S.; Calo, M. M.; Luzio, D.; Dorbath, C.

    2009-12-01

    A procedure to obtain 3D velocity-density models and earthquake relocation by integrated inversion of P and S wave traveltimes and Bouguer anomaly distribution was applied to a large dataset concerning the Southern Tyrrhenian and Sicilian areas. The seismic dataset was subdivided into two subsets for separate inversions, whose results were later on joined by the WAM (Weighted Average Model) technique. This is a post-processing technique proposed by Calò et al. (2009) by which preliminary tomographic models are unified in a common 3D grid. The first dataset concerns 28873 P and 9990 S arrival times of 1800 earthquakes located in the area 14°30‧ E - 17°E, 37°N - 41°N while the second dataset contains 31250 P and 13588 S arrival-times related to 1951 events located in the area 11° E - 15°48‧ E, 36°30‧N - 39°N. The selected events were recorded at least by 10 stations in the period 1981-2005 and marked by RMS < 0.50 s. The second dataset was integrated with P-wave traveltimes picked in several sesmic profiles carried out in the study region. The Bouguer anomaly measurements were interpolated in the nodes of a 8x8 km regular grid covering the area 12° E - 16°01‧ E, 36°13‧ N - 38°31‧ N. The proposed procedure allows to invert seismic and gravimetric data with a sequential technique to avoid the problematic optimization of the relative weights to assign to the different type of data. A first WAM provides a preliminary Vp, Vs and Vp/Vs models and a first ipocentral relocation. Since the obtained Vs model seems poorly constrained by the S wave arrival times, the Vp model is converted in a new Vs model, through a Vs-Vp correlation law proposed by T.M. Brocher (2005), and used, jointly to the Vp model, as input for a second WAM. The results of this second step are used to derive, by the empirical Brocher’s equations, 2 density distributions associated to the Vp and Vs models. These density models are statistically compared and the distribution of

  9. On the isostatic gravity anomaly and disturbance and their applications to Vening Meinesz-Moritz gravimetric inverse problem

    NASA Astrophysics Data System (ADS)

    Sjöberg, Lars E.

    2013-06-01

    In this study, we show that the traditionally defined Bouguer gravity anomaly needs a correction to become `the no-topography gravity anomaly' and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the Bouguer gravity anomaly plus a gravitational compensation effect. This is because only the new isostatic gravity anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic gravity anomaly. We show how the Moho geometry can be solved for the gravity anomaly, gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same.

  10. Sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data

    NASA Astrophysics Data System (ADS)

    Senosy, M. M.; Youssef, M. M.; Abdel Zaher, M.

    2013-06-01

    The Western Desert, Egypt includes the major groundwater aquifer in the country. It is apart from the Major Sahara Nubian Aquifer which is present in Sudan, Chad, Egypt and Libya. Thickness of this aquifer is changed laterally from south to north and also from west to east. The changes may structurally or litheologicalley control. The present study is focused on using of Bouguer gravity anomaly mapped at a scale of 1:500,000 and the lithological logs of about 120 deep wells used to determine the thickness of the sedimentary sequence containing the main Nubian sandstone water aquifer in important area of Egypt. The area is located in the southern part of the Western Desert bounded by the latitudes 22°00'-26°30'N, and longitudes 28°30'-33°00'E. The predominant structures affecting the basement rocks and the sedimentary cover were traced and analyzed. The gravity stripping approach was applied to eliminate the gravity effects caused by sedimentary sequence and to separate density anomalies within the sedimentary fill from the influence of rocks at deeper levels in the crystalline crust. The study indicated that the surface of the basement rocks is highly rugged and mostly controlled by structures which have a direct effect on thickness variation of the sedimentary cover all over the area. Regionally the area is characterized by two major intracratonic basins (the Dahkla Basin and the Nile valley Basin) separated by a NE-SW trending swell of the Kharga uplift and bounded at the south by the Oweinat-Bir Safsaf-Aswan uplift. These major tectonic units are controlled by fault structures trending in N-S, E-W, NE-SW, NW-SE, which cut the basement rocks and extend upward in the sedimentary cover. The maximum thickness of sandstone formations is recorded at west Oweinat, west Kurkur, southwest of Aswan, Gramashin, Dakhla oasis and some localities west of Sohag and Qena towns. At these localities the thickness ranges between 600 and 900 m. As this formation is the main

  11. Constraints on the deep structure and dynamic processes beneath the Alps and adjacent regions from an analysis of gravity anomalies

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, Helene; Molnar, Peter

    1989-01-01

    Gravity anomalies over the Alps and the Molasse Basin are examined, focusing on the relationship between the anomalies and the tectonic processes beneath the region. Bouguer gravity anomalies measured in France, Germany, Italy, and Switzerland are analyzed. No large isostatic anomalies are observed over the Alps and an elastic model is unable to account for gravity anomalies over the Molasse Basin. These results suggest that the dynamic processes that flexed the European plate down, forming the Molasse Basin and building the Alpine chain, have waned. It is proposed that the late Cenozoic uplift of the region may be due to a diminution or termination of downwelling of mantle material.

  12. Conversion of Bouguer Gravity Data to Depth, Dip, And Density Contrast With Complex Attributes Analysis Technique in the Area of Greece.

    NASA Astrophysics Data System (ADS)

    Kavaja, V.; Reci, H.; Tsokas, G.

    2005-05-01

    The complex attributes analysis is an operator used in the extracting parameters of the buried structures with susceptibility and density contrasts distributions, which lead to the gravity and magnetic anomalies in the region of interest. In this paper is presented the complex attributes analysis of gravity field filtered for wavelengths lower than 50 km in the territory of Greece. The area o Greece has a complex tectonic history and fault system dominated by the subduction of the African plate beneath the Euroasia. A Low-pass filter is used on the Bouguer Anomaly to cut off wavelengths lower than 50Km in order to delineate the major faults structures of interests at big depths. The complex attributes technique aids in interpretation of potential field anomalies, because it can delineate the edges of concealed targets. In obtaining the source parameters from the complex attributes like the local depth, strike and dip, the assumption of sloping contact for the subsurface model is used. The estimated local parameters are in agreement with results obtained by previous interpretations. They can be used in combination with other method to interpret the anomalous field.

  13. Comparison of onshore Bouguer anomalies with GOCE Satellite Data in two sections of the Andes: at 29°S and at 39°S.

    NASA Astrophysics Data System (ADS)

    Alvarez, O.; Gimenez, M.; Braitenberg, C.; Martinez, P.

    2012-04-01

    In the present work we compare the Bouguer anomaly obtained from onshore measurements with the Bouguer anomaly obtained from satellite GOCE data along two well known sections of the Andes, at 29°18'S and at 38°45'S. The first gravimetric section, published by Martinez et al. (2006), describes a gravity and altimetric profile that extends over a distance surpassing 800km in Argentina, at 29°18'S. Using gravimetric inversion methods a crustal model was obtained which is in accordance with the main regional geologic structures. This model fits with a dominant collision mechanism that affected ancient blocks and is a two-layer crustal model with lateral density variations. The Chilenia, Cuyania, Famatina System, Pampia and River Plate cratons were detected. From the gravimetric signal we identify beyond doubt the suture zone between the Precordillera and the Famatina System Ranges, as well as the shear zone between the latter ranges and the Velasco Range. The maximum crustal thickness determined beneath the Andean Cordillera at this latitude is 69 km, whereas under the Famatina System and the Velasco Ranges the values obtained are, respectively, 56 km and 46.5 km. The second profile was published by Folguera et al., (2008). The western retroarc of the Southern Andes between 38° and 40°S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4-3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Normal crustal thickness at these latitudes is around 42km, whereas in this part of the retroarc the thickness is less than 32km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath South American plate, which is suggested by a westward shift and narrowing of the arc during the last 5Ma

  14. Gravity Anomalies and Depths of Sedimentary of Mekong Delta Area, South of Vietnam

    NASA Astrophysics Data System (ADS)

    Dang Van, L.

    2014-12-01

    The Mekong Delta is the region in the south of Vietnam with the total area of about 40.000 km2 and almost of this area is covered by water. Gravity measurement of this area was performed by Cuu Long Petroleum Agency (Vietnam) in 1980's and the Bouguer anomaly map of this area at the scale of 1/500.000 was established.We used the Bouguer anomaly map to study the geological structure of this area. This paper is divided into two parts. Firstly, we split the Mekong Delta area into two basins (CanTho-DongThap and TraCu basins) and two swells (Saigon and SocTrang swells) and delineated their boundaries by using the characteristics of Bouguer anomalies. Secondly, we used the second polynomial formula to separate the Bouger anomaly map into the regional and residual gravity anomaly maps. With this residual anomaly map, the 3D basemenf of Cenozoic-Mesozoic sediments of this area was computed by using the Parker-Oldenburg method.

  15. Upward Continuation Apply Newly to Process Gravity Anomaly Data in the East China Sea

    NASA Astrophysics Data System (ADS)

    Han, Bo; Zhang, Xunhua; Jiang, Jinyu

    2014-05-01

    The research area lies in the East China Sea and its adjacent area and the concrete is between 120-130 degree of east longitude and 20-30 degree of north latitude and it also lies between Eurasian Plate and Pacific Plate. The structures of the area transform differently and they are namely Uplifted Zone of Zhejiang-Fujian, East China Sea Shelf Basin, Okinawa Trough Back-arc Basin, Ryukyu Arc, Ryukyu trench and Philippine Sea from west to east. Bouguer gravity anomaly can reflect deep structure characters and it is help to judge deep structures. The bouguer gravity anomalies of the area change differently from west to east. The anomalies increase gradually from land to the middle of Okinawa trough and near land anomaly contour strike accords with coastline and the middle of Okinawa trough reflect the highest anomalies in this area. Gravity anomalies re-increase from Ryukyu fore-arc basin to trench and Ryukyu island arc appears the low anomalies. Philippine Sea appears high gravity anomalies background. Upward continuation method has been used to process original gravity anomaly as a common method and its destination is to weaken local anomaly and at last strengthen deep anomaly and it's important to deep structure study. Upward 5 km, 10 km and 20 km have been used to process data and the results been compared. However, the research area is very large and the deep structure is complex, it isn't suitable to use single height to upward continuation processing bouguer gravity anomaly. Then we propose multiple upward heights continuation to process gravity data respectively in different area. We use upward 20km to process data in the area from land to the slope and upward 10km from Okinawa trough to Ryukyu island arc and upward 5km from Ryukyu trench to Philippine Sea. At last we obtain multiple upward height result and the calculated result confirms that it is fit to use this method. Gravity anomalies contours become smoother than before and the deep structures become

  16. Interpretation of gravity anomalies in the northwest Adirondack lowlands, northern New York

    SciTech Connect

    Revetta, F.A.; O'Brian, B. . Geology Dept.)

    1993-03-01

    Twelve hundred gravity measurements were made in the Adirondack Highlands and northwest Adirondack Lowlands, New York between 44[degree]15 minutes and 44[degree]30 minutes N. Latitude and 75[degree]00 minutes W. Longitude. A Bouguer gravity map constructed from the gravity measurements includes the Carthage-Colton Mylonite Zone, a major structural boundary between the highlands and lowlands. The gravity map indicates the gravity contours trend parallel to the CCMZ along most of its length however in some areas the contours cross the boundary. No clear-cut relationships exists between the CCMZ and gravity contours. The Bouguer gravity map shows several prominent gravity anomalies which correlate with the geology seismicity and mineral deposits in the area. Gravity lows of 20 to 30 g.u. are centered over the Gouverneur, Hyde and Payne Lake Alaskite gneiss bodies. A gravity high of 20 g.u. occurs over the Pleasant Lake gabbro pluton. Gravity highs of 35 and 100 g.u. occur over the Sylvia Lake Zinc District and marble just north of the district. A gravity high at Russell, N.Y. coincides with a cluster of nine earthquake epicenters. Finally a steep gravity gradient separates high density rocks from lower density rocks along the Black Lake fault. Two-dimensional computer modeling of the geologic features is underway and quantitative models of the structures will be presented.

  17. Deformation induced topographic effects in inversion of temporal gravity changes: First look at Free Air and Bouguer terms

    NASA Astrophysics Data System (ADS)

    Vajda, Peter; Zahorec Pavol, Pavol; Papčo, Juraj; Kubová, Anna

    2015-06-01

    We review here the gravitational effects on the temporal (time-lapse) gravity changes induced by the surface deformation (vertical displacements). We focus on two terms, one induced by the displacement of the benchmark (gravity station) in the ambient gravity field, and the other imposed by the attraction of the masses within the topographic deformation rind. The first term, coined often the Free Air Effect (FAE), is the product of the vertical gradient of gravity (VGG) and the vertical displacement of the benchmark. We examine the use of the vertical gradient of normal gravity, typically called the theoretical or normal Free Air Gradient (normal FAG), as a replacement for the true VGG in the FAE, as well as the contribution of the topography to the VGG. We compute a topographic correction to the normal FAG, to offer a better approximation of the VGG, and evaluate its size and shape (spatial behavior) for a volcanic study area selected as the Central Volcanic Complex (CVC) on Tenerife, where this correction reaches 77% of the normal FAG and varies rapidly with terrain. The second term, imposed by the attraction of the vertically displaced topo-masses, referred to here as the Topographic Deformation Effect (TDE) must be computed by numerical evaluation of the Newton volumetric integral. As the effect wanes off quickly with distance, a high resolution DEM is required for its evaluation. In practice this effect is often approximated by the planar or spherical Bouguer deformation effect (BDE). By a synthetic simulation at the CVC of Tenerife we show the difference between the rigorously evaluated TDE and its approximation by the planar BDE. The complete effect, coined here the Deformation Induced Topographic Effect (DITE) is the sum of FAE and TDE. Next we compare by means of synthetic simulations the DITE with two approximations of DITE typically used in practice: one amounting only to the first term in which the VGG is approximated by normal FAG, the other adopting a

  18. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

  19. Thickness variation of the sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data using neural network method

    NASA Astrophysics Data System (ADS)

    Abdel Zaher, M.; Senosy, M. M.; Youssef, M. M.; Ehara, S.

    2009-06-01

    The Bouguer anomaly map of scale 1:500,000 and the lithological logs of more than 120 deep wells distributed in the Southern part of Western Desert of Egypt were used to determine the thickness of the sedimentary cover containing the main sandstone water formation. The predominant structures affecting both the basement rock and the sedimentary cover were also studied. Gravity stripping approach was applied to separate density anomalies within the sedimentary fill from the influence of deeper levels in the crystalline crust. The study indicated that the surface of the basement rock is highly rugged and mostly controlled by structures causing variation of the sedimentary cover thickness from location to other all over the area. Isopach maps were constructed based on the Artificial Neural Network (ANN) model which is considered a best method for that operation. The maximum thickness of sandstone formations is recorded at west Oweinat, southwest of Aswan, Dakhla oasis and west of Qena town. As this formation is the main water aquifer in the study area, therefore these locations are characterized by the presence of huge amount of ground water. Accordingly, these areas must be taking the priority in the programs of sustainable development in southern Egypt.

  20. Bouguer Images of the North American Craton

    NASA Technical Reports Server (NTRS)

    Arvidson, R. E.; Bindschadler, D.; Bowring, S.; Eddy, M.; Guinness, E.; Leff, C.

    1985-01-01

    Processing of existing gravity and aeromagnetic data with modern methods is providing new insights into crustal and mantle structures for large parts of the United States and Canada. More than three-quarters of a million ground station readings of gravity are now available for this region. These data offer a wealth of information on crustal and mantle structures when reduced and displayed as Bouguer anomalies, where lateral variations are controlled by the size, shape and densities of underlying materials. Digital image processing techniques were used to generate Bouguer images that display more of the granularity inherent in the data as compared with existing contour maps. A dominant NW-SE linear trend of highs and lows can be seen extending from South Dakota, through Nebaska, and into Missouri. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.

  1. New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica

    NASA Astrophysics Data System (ADS)

    Scheinert, M.; Ferraccioli, F.; Schwabe, J.; Bell, R.; Studinger, M.; Damaske, D.; Jokat, W.; Aleshkova, N.; Jordan, T.; Leitchenkov, G.; Blankenship, D. D.; Damiani, T. M.; Young, D.; Cochran, J. R.; Richter, T. D.

    2016-01-01

    Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.

  2. Complete Bouguer gravity map of the Nevada Test Site and vicinity, Nevada

    SciTech Connect

    Healey, D.L.; Harris, R.N.; Ponce, D.A.; Oliver, H.W.

    1987-12-31

    About 15,000 gravity stations were used to create the gravity map. Gravity studies at the Nevada Test Site were undertaken to help locate geologically favorable areas for underground nuclear tests and to help characterize potential high-level nuclear waste storage sites. 48 refs. (TEM)

  3. Gravity anomalies, spatial variation of flexural rigidity, and role of inherited crustal structure in the Aquitaine Basin

    NASA Astrophysics Data System (ADS)

    Angrand, Paul; Ford, Mary; Watts, Anthony; Bell, Rebecca E.

    2016-04-01

    The Aquitaine foreland basin developed from Campanian to Miocene by flexure of the upper (European) plate during the Pyrenean orogeny. The foreland basin forms a syn-orogenic sedimentary wedge up to 6 km thick in the south, thinning rapidly north and has a maximum width of 200 km in the west. The flexural basin was superimposed on a lithosphere previously affected by Apto-Albian hyper-extension. What are the effects of an inherited extremely weak and narrow rifted zone on the behavior of a superimposed flexural foreland basin? Coupled with surface and subsurface data, Bouguer gravity anomalies were used to determine the crustal structure of the northern Pyrenean retrowedge and the flexure of the European plate. In the centre, the basin shows a regional Bouguer anomaly pattern typical of foreland basins with the maximum of syn-orogenic deposits corresponding to a low and the forebulge to a high. However, south of the North Pyrenean Frontal Thrust (NPFT) this regional field is overprinted by strong positive Bouguer anomalies, which correspond to high density bodies (mantle or lower crust) transported along the NPFT. Stratigraphy shows that the central basin evolved as a series of narrow, laterally variable depocentres that migrated north. Shortening is accommodated mainly by thick skinned deformation and local reactivation of salt structures. In the east, the Toulouse Fault separates the central and eastern foreland. The eastern foreland shows a broader zone of negative Bouguer values. This foreland is salt-free and stratigraphy records higher subsidence. The easternmost basin is completely overprinted by the opening of the Gulf of Lion. In the west, the foreland does not show a typical regional gravity anomaly pattern due to overprinting by the opening of the Bay of Biscay. Instead, a major gravity high is centered on the northern Landes High, with a second high centered on the Labourd massif south of the NPFT. Neither the Parentis rift basin nor the salt

  4. Consistent anomalies of the induced W gravities

    NASA Astrophysics Data System (ADS)

    Abud, Mario; Ader, Jean-Pierre; Cappiello, Luigi

    1996-02-01

    The BRST anomaly which may be present in the induced Wn gravity quantized on the light-cone is evaluated in the geometrical framework of Zucchini. The cocycles linked by the cohomology of the BRST operator to the anomaly are straightforwardly calculated thanks to the analogy between this formulation and the Yang-Mills theory. We give also a conformally covariant formulation of these quantities including the anomaly, which is valid on arbitrary Riemann surfaces. The example of the W3 theory is discussed and a comparison with other candidates for the anomaly available in the literature is presented.

  5. Gravity and magnetic anomalies of the Cyprus arc and tectonic implications

    NASA Astrophysics Data System (ADS)

    Ergün, M.; Okay, S.; Sari, C.; Oral, E. Z.

    2003-04-01

    In present day, eastern Mediterranean is controlled by the collision of the African and Eurasian plates and displacements of Arabian, Anatolian and Aegean micro-plates. The boundary between African and Eurasian plates is delineated by the Hellenic arc and Pliny-Strabo trench in the west and the Cyprus arc and a diffuse fault system of the Eastern Anatolian Fault zone in the east. The available gravity and magnetic data from the easternmost Mediterranean allow to subdivide this basin into three provinces: the northeastern Mediterranean north of the Cyprus Arc; the Levant Basin south of the Cyprus Arc and east of the line that roughly continues the Suez rift trend toward the Gulf of Antalya, between Cyprus and Anaximander Mountains; and the Mediterranean Ridge, Herodotus Basin west of this line. High anomalies observed in Cyprus and the sea region at the south is prominent in the gravity data. The Bouguer gravity anomaly reaches its maximum values over Cyprus, where it is most probably caused by high dense Troodos ophiolites. The uplifted oceanic crust causes high Bouguer anomaly also seen in the vicinity of Eratosthenes Seamount. Another result obtained from gravity data is that the crust under Herodotos and Rhodes basins is somehow oceanic and Anaximander, Eratosthenes and Cyprus are continental fragments. There are no linear magnetic anomalies in the Mediterranean. But there are magnetic anomalies over the Eratosthenes seamount and as well as from Cyprus to the Antalya basin due to the ophiolitic bodies. In Cyprus, the last compressional deformations were defined near the Miocene/Pliocene boundary. The extensional deformation associated with the Antalya basin appears to be separated by a zone of the Florence rise and Anaximander Mountains affected by differential tectonic movements. Eratosthenes Seamount is a positive crustal feature in the process of collision with Cyprus along an active margin; there is clearly a potential tectonic relationship to the onland

  6. Newberry Combined Gravity 2016

    DOE Data Explorer

    Kelly Rose

    2016-01-22

    Newberry combined gravity from Zonge Int'l, processed for the EGS stimulation project at well 55-29. Includes data from both Davenport 2006 collection and for OSU/4D EGS monitoring 2012 collection. Locations are NAD83, UTM Zone 10 North, meters. Elevation is NAVD88. Gravity in milligals. Free air and observed gravity are included, along with simple Bouguer anomaly and terrain corrected Bouguer anomaly. SBA230 means simple Bouguer anomaly computed at 2.30 g/cc. CBA230 means terrain corrected Bouguer anomaly at 2.30 g/cc. This suite of densities are included (g/cc): 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.67.

  7. Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion.

    PubMed

    Tolstoy, M; Harding, A J; Orcutt, J A

    1993-10-29

    Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33 degrees S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data. PMID:17812339

  8. Magnetic and gravity anomalies in the Americas

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    The cleaning and magnetic tape storage of spherical Earth processing programs are reported. These programs include: NVERTSM which inverts total or vector magnetic anomaly data on a distribution of point dipoles in spherical coordinates; SMFLD which utilizes output from NVERTSM to compute total or vector magnetic anomaly fields for a distribution of point dipoles in spherical coordinates; NVERTG; and GFLD. Abstracts are presented for papers dealing with the mapping and modeling of magnetic and gravity anomalies, and with the verification of crustal components in satellite data.

  9. Gravity anomaly detection: Apollo/Soyuz

    NASA Technical Reports Server (NTRS)

    Vonbun, F. O.; Kahn, W. D.; Bryan, J. W.; Schmid, P. E.; Wells, W. T.; Conrad, D. T.

    1976-01-01

    The Goddard Apollo-Soyuz Geodynamics Experiment is described. It was performed to demonstrate the feasibility of tracking and recovering high frequency components of the earth's gravity field by utilizing a synchronous orbiting tracking station such as ATS-6. Gravity anomalies of 5 MGLS or larger having wavelengths of 300 to 1000 kilometers on the earth's surface are important for geologic studies of the upper layers of the earth's crust. Short wavelength Earth's gravity anomalies were detected from space. Two prime areas of data collection were selected for the experiment: (1) the center of the African continent and (2) the Indian Ocean Depression centered at 5% north latitude and 75% east longitude. Preliminary results show that the detectability objective of the experiment was met in both areas as well as at several additional anomalous areas around the globe. Gravity anomalies of the Karakoram and Himalayan mountain ranges, ocean trenches, as well as the Diamantina Depth, can be seen. Maps outlining the anomalies discovered are shown.

  10. Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2015-04-01

    Isostaic anomalies represent one of the most useful "geological" reduction of the gravity field. With the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  11. Gravity and magnetic anomaly data analysis

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1982-01-01

    Progress on the analysis MAGSAT data is reported. The MAGSAT data from 40 deg S to 70 deg N latitude and 30 deg W to 60 E longitude was reduced to radial polarization. In addition, gravity anomaly data from this area were processed and a variety of filtered maps were prepared for combined interpretation of the gravity and magnetic data in conjunction with structural and tectonic maps of the area. The VERSATEC listings and cross-reference maps of variable and array names for the spherical Earth analysis programs NVERTSM, SMFLD, NVERTG, and GFLD were also prepared.

  12. The Origin of the Rodrigues Depth Anomaly: New constraints from integrated gravity inversion

    NASA Astrophysics Data System (ADS)

    Minakov, Alexander; Gaina, Carmen; Faleide, Jan Inge

    2016-04-01

    This study is focused on the Western Indian Ocean including the Central Indian Ridge. The Rodrigues Ridge is a bathymetric feature (500 km -long and 20 km -wide) situated east of the Mascarene Plateau and Mauritius, with an oblique trend with respect to the underlying seafloor spreading fabric. The trend is also different from the fracture zone and hotspot tracks in this area. The region where the Rodrigues Ridge intersects the Central Indian Ridge is characterized by broad area being shallower than it should be according to standard age-depth relations for oceanic basement. With this contribution we aim to determine key factors controlling the formation of the Rodrigues Ridge and the development of the depth anomaly through time. In order to better constrain the nature and extent of the depth anomaly underlying the Rodrigues Ridge and surrounding region, we have carried out a 3D gravity and bathymetry data analysis. This analysis included an iterative gravity inversion approach linked to the computation of residual topography through the temperature and density model of the crust and upper mantle. We use a refined plate kinematic model of the study area for the time period ca. 30 Ma to the present. The refined kinematic model is an important element for temperature modelling at the ridge-transform intersection. Existing seismological data provide additional constraints for the gravity inversion. The results of the 3D gravity and bathymetry data analysis support the model of enhanced production of crust at the Central Indian Ridge adjacent to the Rodrigues Ridge. The depth anomaly is composed of abrupt Rodrigues Ridge edifice sitting on top a relatively smooth and broad anomaly characterized by crustal thickness between 8 and 13 km. These values are significantly higher than those typical for the crustal thickness generated by slow seafloor spreading at the Central Indian Ridge and other slow spreading ridges. This gives rise to a large negative residual mantle

  13. Trace anomaly and counterterms in designer gravity

    NASA Astrophysics Data System (ADS)

    Anabalón, Andrés; Astefanesei, Dumitru; Choque, David; Martínez, Cristián

    2016-03-01

    We construct concrete counterterms of the Balasubramanian-Kraus type for Einstein-scalar theories with designer gravity boundary conditions in AdS4, so that the total action is finite on-shell and satisfy a well defined variational principle. We focus on scalar fields with the conformal mass m 2 = -2 l -2 and show that the holographic mass matches the Hamiltonian mass for any boundary conditions. We compute the trace anomaly of the dual field theory in the generic case, as well as when there exist logarithmic branches of non-linear origin. As expected, the anomaly vanishes for the boundary conditions that are AdS invariant. When the anomaly does not vanish, the dual stress tensor describes a thermal gas with an equation of state related to the boundary conditions of the scalar field. In the case of a vanishing anomaly, we recover the dual theory of a massless thermal gas. As an application of the formalism, we consider a general family of exact hairy black hole solutions that, for some particular values of the parameters in the moduli potential, contains solutions of four-dimensional gauged {N}=8 supergravity and its ω-deformation. Using the AdS/CFT duality dictionary, they correspond to triple trace deformations of the dual field theory.

  14. Determination of mean gravity anomalies in the Taiwan Island

    NASA Technical Reports Server (NTRS)

    Chang, Ruey-Gang

    1989-01-01

    The fitting and proper regression coefficients were made of one hundred seventeen 10 x 10' blocks with observed gravity data and corresponding elevation in the Taiwan Island. To compare five different predicted models, and the proper one for the mean gravity anomalies were determined. The predicted gravity anomalies of the non-observed gravity blocks were decided when the coefficients obtained through the model with the weighted mean method. It was suggested that the mean gravity anomalies of 10 x 10' blocks should be made when comprehensive the observed and predicted data.

  15. Tertiary basin-and-range structure in Southern Nevada-Utah-Arizona region via borehole, seismic reflection, and Bouguer gravity data: Insights on hydrocarbon potential

    SciTech Connect

    Carpenter, D.G.

    1988-01-01

    Extension characterized by full grabens and half-grabens and tilted, folded, and faulted range blocks is geometrically and kinematically constrained by geologic and geophysical data. Rootless gravity-slide blocks are common secondary features to high-angle normal faults, which exert primary control over crustal extension. A synthetic seismogram from the only test well (Mobil Virgin River 1-A; TD = 5,962.5m), seismic reflection, and Bouguer gravity data (up to 70 mgal of relief) indicate over 7,600m of low-density Tertiary sediments in the Virgin Valley basin. Several thousand meters of sediment are within the oil-generative window. Neogene basalt flows suggest geothermal gradients higher than today. Lacustrine limestone in the Oliocene-Miocene Horse Spring Formation contains cryptalgalaminate, a potential hydrocarbon source. The Horse Spring Formation is overlain unconformably by the Miocene-Pliocene Muddy Creek Formation. These formations were deposited in association with movement on the Virgin-Beaver Dam Mountains fault, as indicated by fanning-upward reflector geometry. The formations are incorporated into a major rollover anticline. Mississippian Chainman Shale, penetrated to the west by Chevron's Colorock Quarry well, indicates a possibility for Sevier-age hydrocarbon generation by thrust loading.

  16. Spectral analysis of gravity anomalies and the architecture of tectonic wedging, NE Venezuela and Trinidad

    NASA Astrophysics Data System (ADS)

    Russo, R. M.; Speed, R. C.

    1994-06-01

    We have analyzed the spectral content of free air gravity anomalies in the Caribbean-South American plate boundary zone in order to determine better the near-surface (0-120 km) distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region. The plate boundary zone in northeastern Venezuela and Trinidad is the site of the world's sea level continental minimum of Bouguer gravity anomalies, yet the region is also one of mild topography (mean value 43 m, maximum 1200 m). We find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone. We interpret interfaces at 30-35 km and 32 km beneath the Guyana Shield and the Aves Ridge, respectively, to be the Moho. Other shallow interfaces (5-14 km) are most likely sediment cover-basement contacts in the Maturin foreland basin and southern Grenada Basin. Deeper interfaces (54-63 km) we associate with loaded and downwarped continental and oceanic South American lithosphere. The deepest boundaries, at depths of 89-120 km, may be related to detached or detaching oceanic lithosphere overridden by continental South America. We use our results to test the tectonic wedging model of the plate boundary zone recently published by Russo and Speed (1992). We find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner Guyana Shield crust.

  17. Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  18. Upgraded gravity anomaly base of the United States

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Kucks, R.; Roman, D.; Hittelman, A.M.

    2002-01-01

    A concerted effort to compile an upgraded gravity anomaly database, grid, and map for the United States by the end of 2002 is under way. This effort can be considered as the first step in building a data system for gravity measurements, and it builds on existing collaborative efforts. This paper outlines the strategy for assembling the individual map and digital products related to the United States gravity database.

  19. Validation of South American terrestrial gravity anomalies by GOCE

    NASA Astrophysics Data System (ADS)

    Fecher, Thomas; Pail, Roland; Gruber, Thomas; Holmes, Simon

    2015-04-01

    Since its launch in 2009, ESA's GOCE mission has generated high-accuracy gravity field information, of near-global coverage, for the long- to medium-wavelength part of the gravity field (<=degree/order 260). These highly accurate gravity data are especially important for regions such as South America, Africa or Asia, where coverage and/or accuracy of alternate data sets, mostly gravimetry, are relatively poor. In these regions, the GOCE data can be useful in identifying and assessing suspect terrestrial data. Specifically, in coordination with partner organizations, we are already leveraging satellite gravity field missions to identify inconsistencies between different regional gravity anomaly data sets. Many of these inconsistencies relate to data quality issues. Resolving these issues better enables the terrestrial gravity data to strengthen and correct the satellite gravity models at their higher end (degree/order 200 to 260). The harmonization between terrestrial and satellite datasets reduces the commission error in gravity modeling over the associated range. Remaining issues not related to data quality can then be isolated for additional study. For example, a host of geophysical and temporal issues may be contributing to irregularities. In this paper, the quality of a South America data set of gravity anomalies shall be analyzed. The accuracy of the gravity anomalies shall be assessed, and systematic errors shall be detected. For this purpose, consistent gravity field corrections have to be applied. The aim of the revision of the data set is to exclude bad data and to provide accuracies which can serve as a stochastic model in the frame of a combined solution. By this procedure, the performance of a gravity field model based on the combination of satellite and terrestrial observations should be improved for South America.

  20. Spectral Correlation of Antarctic Satellite Magnetic and Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Wells, S. B.; von Frese, R. R.; Kim, H.; Potts, L.; Kim, J.; Gaya-Pique, L. R.

    2005-05-01

    Large areas of the Antarctic continent lack terrestrial or airborne magnetic and gravity survey coverage due to the harsh climate and extended distances involved. Satellite missions therefore play an important role, often being the only source of information for the study of remote regions. NASA's GRACE satellite mission provides global-scale gravity measurements with a much higher spatial resolution than previous missions. The free-air gravity anomalies in Antarctica from GRACE offer new insights on the poorly understood Antarctic crust. New interpretations and candidates for further investigation are presented from spectral correlation analysis between the new GRACE free-air gravity anomalies and magnetic anomalies measured by the CHAMP and Ørsted satellites. We quantify the anomaly correlations using correlation filters based on Poisson's relation. Favorability indices are derived that highlight the positive and negative correlations between the satellite observed geopotential anomalies. Several positively and negatively correlated regional anomalies yield new insights on the enigmatic crustal tectonics of Queen Maud Land, Enderby Land and other regions of East Antarctica, and the West Antarctic Peninsula.

  1. Study of gravity and magnetic anomalies using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.

  2. Detailed gravity anomalies from GEOS-3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1978-01-01

    A technique for deriving mean gravity anomalies from dense altimetry data was developed. A combination of both deterministic and statistical techniques was used. The basic mathematical model was based on the Stokes' equation which describes the analytical relationship between mean gravity anomalies and geoid undulations at a point; this undulation is a linear function of the altimetry data at that point. The overdetermined problem resulting from the excessive altimetry data available was solved using Least-Squares principles. These principles enable the simultaneous estimation of the associated standard deviations reflecting the internal consistency based on the accuracy estimates provided for the altimetry data as well as for the terrestrial anomaly data. Several test computations were made of the anomalies and their accuracy estimates using GOES-3 data.

  3. Approximating edges of source bodies from magnetic or gravity anomalies.

    USGS Publications Warehouse

    Blakely, R.J.; Simpson, R.W.

    1986-01-01

    Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors

  4. Magnetic and gravity anomalies of the slow-spreading system in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Nakanishi, M.; Fujimoto, H.; Tamaki, K.; Okino, K.

    2002-12-01

    The spreading system in the Gulf of Aden between Somalia, NE Africa, and Arabia has an ENE-WSW trend and its half spreading rate is about 1.0 cm/yr (e.g., Jestin et al., 1994). Previous studies (e.g., Tamsett and Searle, 1988) provided the general morphology of the spreading system. To reveal detailed morphology and tectonics of the spreading system in the Gulf of Aden, geophysical investigation was conducted along the spreading system between 45°30OE and 50°20OE by the R/V Hakuho-maru from December 2000 to January 2001. Bathymetric data were collected using an echo sounder SEA BEAM 2120 aboard R/V Hakuho-maru. Magnetic and gravity data were collected by towed proton magnetometer and shipboard gravimeter, respectively. The strike of the spreading centers east of 46°30OE is N65°W. The topographic expression of the spreading centers east of N46°30OE is an axial rift valley offset by transform faults siilar to that observed at slow spreading centers in other areas. The bathymetric feature of the spreading centers between 45°50OE and 46°30OE with a strike N80°E is N65°W trending en-echelon basins. The spreading center west of 45°50OE with a strike E-W is bouned by linear ridges and its bathymetric expression is N65°W trending en-echelon ridges. The axial rift valley west of N46°30OE is not offset by any prominent transform faults. Negative magnetic anomaly is dominant over the axial valleys. Its amplitude is about 500 nT and the wavelength is about 30 km. Prominent linear negative magnetic anomaly, which is more than 1000 nT, exists west of N46°30OE. The strike of the linear magnetic anomaly correlates with that of axial valleys west of N46°30OE. Mantle Bouguer gravity anomaly of the spreading centers increases eastward. This trend correlates with the eastward deepening of spreading centers.

  5. Crustal structure and gravity anomalies beneath the Rif, northern Morocco: implications for the current tectonics of the Alboran region

    NASA Astrophysics Data System (ADS)

    Petit, Carole; Le Pourhiet, Laetitia; Scalabrino, Bruno; Corsini, Michel; Bonnin, Mickael; Romagny, Adrien

    2015-04-01

    We analyze Bouguer anomaly data and previously published Moho depths picked from receiver functions in order to determine the amount of isostatic compensation or un-compensation of the Rif topography in northern Morocco. We use Moho depth variations extracted from receiver function analyses to predict synthetic Bouguer anomalies that are then compared to observed Bouguer anomaly. We find that Moho depth variations due to isostatic compensation of topographic and/or intracrustal loads do not match Moho depth estimates obtained from receiver function analyses. The isostatic misfit map evidences excess crustal root as large as 15 km in the western part of the study area, whereas a "missing" crustal root appears east of 4.3°E. Given crustal thickness provided by reciever function data, we estimated the amount of "missing" topography (in a local isostatic sense) in the Western Rif at 1000±500 m depending on the assumed crust-mantle density contrast, i.e. twice to four times lower than the actual Rif highest elevation (>2000m). Therefore, without this negative dynamic effect, the Rif topography would be higher by 25% to 75% compared to its actual elevation. This excess root/ missing topography correlates with the presence of a dense mantle lid, the noticeable south-westward drift of the Western Rif area, and with a current surface uplift.Integrating gravity data, crustal thickness from reciever functions, seismic tomography, GPS and geologic models, we propose that local thickening of the crust corresponds to the dynamic response to the delaminated mantle lid that is progressively detaching westward or south-westward from the overlying crust. In this model, provided the lower crust is sufficiently buoyant and weak, the inward flow of lower crust towards the mantle hinge can cause a positive isostatic topography that is larger than the negative dynamic topography created by the sinking mantle lid. According to this hypothesis, the long wavelength Rif topography can be

  6. Gravity anomalies and deep structure of eastern Hudson bay

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Manoj; Gibb, R. A.

    1981-01-01

    The Cape Smith and Belcher foldbelts of Lower Proterozoic (Aphebian) rocks form parts of the proposed Circum-Superior suture which separates the Superior and Churchill structural provinces of the Canadian Shield. Recent marine gravity surveys in eastern Hudson Bay (1976-1979) show that the distinctive linear gravity pattern of paired positive and negative anomalies along the Cape Smith foldbelt of northern Ungava extends southwards into Hudson Bay to the Belcher Islands. Interpretation of five gravity profiles across the Cape Smith and Belcher foldbelts suggests that the Churchill crust is thicker and denser than the Superior. The boundary between the two contrasting crustal blocks is interpreted as a collisional suture. The rocks of the foldbelts which are progressively more volcanic northwards are the source of a residual positive anomaly associated with the Cape Smith foldbelt and a series of discontinuous positive residual anomalies in the Bay. To the north the thicknesses of the foldbelt rocks are estimated to be between 4 and 9 km with a local maximum of 13 km in the northernmost profile. To the south in the Belcher Islands, where geological estimates of formation thickness and measured rock densities provide more constraints on the interpretation of the residual anomalies, the foldbelt rocks are generally 6-7 km thick with a local maximum thickness of about 9 km. One possible interpretation of paleomagnetic results for Belcher Islands rocks in terms of a two-plate model lends support to the collision hypothesis.

  7. Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Gao, Rui; Guo, Xiaoyu

    2016-04-01

    The eastern Tibetan plateau has been getting more and more attention because it combines active faults, uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus, a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative (THD) had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks, including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the Songpan-Garze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion, which is coincident with the flowing direction indicated from the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

  8. Gravity anomalies without geomagnetic disturbances interfere with pigeon homing--a GPS tracking study.

    PubMed

    Blaser, Nicole; Guskov, Sergei I; Entin, Vladimir A; Wolfer, David P; Kanevskyi, Valeryi A; Lipp, Hans-Peter

    2014-11-15

    The gravity vector theory postulates that birds determine their position to set a home course by comparing the memorized gravity vector at the home loft with the local gravity vector at the release site, and that they should adjust their flight course to the gravity anomalies encountered. As gravity anomalies are often intermingled with geomagnetic anomalies, we released experienced pigeons from the center of a strong circular gravity anomaly (25 km diameter) not associated with magnetic anomalies and from a geophysical control site, equidistant from the home loft (91 km). After crossing the border zone of the anomaly--expected to be most critical for pigeon navigation--they dispersed significantly more than control birds, except for those having met a gravity anomaly en route. These data increase the credibility of the gravity vector hypothesis. PMID:25392461

  9. On global gravity anomalies and two-scale mantle convection

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.; Marsh, J. G.

    1976-01-01

    The two-scale model of mantle convection developed by Richter and Parsons (1975) predicts that if the depth of the convective layer is about 600 km, then for a plate moving at 10 cm/yr, longitudinal convective rolls will be produced in about 50 million years, and the strike of these rolls indicates the direction of motion of the plate relative to the upper mantle. The paper tests these predictions by examining a new global free air gravity model complete to the 30th degree and order. The free air gravity map developed shows a series of linear positive and negative anomalies (with transverse wavelengths of about 2000 km) spanning the Pacific Ocean, crossing the Pacific rise and striking parallel to the Hawaiian seamounts. It is suggested that the pattern of these anomalies may indicate the presence of longitudinal convective rolls beneath the Pacific plates, a result which tends to support the predictions of Richter and Parsons.

  10. New analytic solutions for modeling vertical gravity gradient anomalies

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Sep; Wessel, Paul

    2016-05-01

    Modern processing of satellite altimetry for use in marine gravimetry involves computing the along-track slopes of observed sea-surface heights, projecting them into east-west and north-south deflection of the vertical grids, and using Laplace's equation to algebraically obtain a grid of the vertical gravity gradient (VGG). The VGG grid is then integrated via overlapping, flat Earth Fourier transforms to yield a free-air anomaly grid. Because of this integration and associated edge effects, the VGG grid retains more short-wavelength information (e.g., fracture zone and seamount signatures) that is of particular importance for plate tectonic investigations. While modeling of gravity anomalies over arbitrary bodies has long been a standard undertaking, similar modeling of VGG anomalies over oceanic features is not commonplace yet. Here we derive analytic solutions for VGG anomalies over simple bodies and arbitrary 2-D and 3-D sources. We demonstrate their usability in determining mass excess and deficiency across the Mendocino fracture zone (a 2-D feature) and find the best bulk density estimate for Jasper seamount (a 3-D feature). The methodologies used herein are implemented in the Generic Mapping Tools, available from gmt.soest.hawaii.edu.

  11. Gravity anomalies in Silurian pinnacle reef trend, southwestern Indiana

    SciTech Connect

    Malinconico, L.L. Jr.; Gognat, T.A.; Scher, P.L. )

    1989-08-01

    Structures produced over the top or along the margins of Silurian Pinnacle reefs have proven to be the source of significant oil production in the eastern Illinois basin. The authors have been able to refine gravity methods that can assist in the exploration of such reef targets. A gravity/density model was developed by combining the 1980 work of Dana at the Wilfred pool (Sullivan County, Indiana) with other lithologic and log data in southwestern Indiana. This model includes the density differences between the reef facies and surrounding lithologies as well as density variations that are the result of compaction of the sedimentary sequence above the reef. The density models suggest that positive gravity anomalies with amplitude between 1.5 to 2.5 mgals might occur over the reefs.

  12. Gravity survey of the southwestern part of the sourthern Utah geothermal belt

    SciTech Connect

    Green, R.T.; Cook, K.L.

    1981-03-01

    A gravity survey covering an area of 6200 km/sup 2/ was made over the southwestern part of the southern Utah geothermal belt. The objective of the gravity survey is to delineate the geologic structures and assist in the understanding of the geothermal potential of the area. A total of 726 new gravity stations together with 205 existing gravity stations, are reduced to give: (1) a complete Bouguer gravity anomaly map, and (2) a fourth-order residual gravity anomaly map; both maps have a 2-mgal contour interval. The complete Bouguer gravity anomaly map shows an east-trending regional gravity belt with a total relief of about 70 mgal which crosses the central portion of the survey area. The gravity belt is attributed to a crustal lateral density variation of 0.1 gm/cc from a depth of 5 to 15 km.

  13. The quest for the perfect gravity anomaly: Part 2 - Mass effects and anomaly inversion

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Hinze, W. J.; Li, X.; Ravat, D.; Webring, M.

    2006-01-01

    Gravity anomalies have become an important tool for geologic studies since the widespread use of high-precision gravimeters after the Second World War. More recently the development of instrumentation for airborne gravity observations, procedures for acquiring data from satellite platforms, the readily available Global Positioning System for precise vertical and horizontal control, improved global data bases, and enhancement of computational hardware and software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases that are made available to the geoscience community by broadening their observational holdings and increasing the accuracy and precision of the included data. Currently the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States of America are being revised using new formats and standards. The objective of this paper is to describe the use of the revised standards for gravity data processing and modeling and there impact on geological interpretations. ?? 2005 Society of Exploration Geophysicists.

  14. Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

    PubMed Central

    Blaser, Nicole; Guskov, Sergei I.; Meskenaite, Virginia; Kanevskyi, Valerii A.; Lipp, Hans-Peter

    2013-01-01

    The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates. PMID:24194860

  15. Gravity anomalies, forearc morphology and seismicity in subduction zones

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Watts, A. B.; Das, S.

    2012-12-01

    We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude trench-normal topographic and free-air gravity anomaly "high" and "low" associated with subduction zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all subduction boundaries on Earth has enabled a classification of these grids with particular emphasis placed on topography and gravity anomalies observed in the region above the shallow seismogenic portion of the plate interface. The isostatic compensation of these anomalies is investigated using 3D calculations of the gravitational admittance and coherence. In the shallow region of the megathrust, typically within 100 km from the trench, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/subducting relief in the form of seamounts and other bathymetric features. While most of these anomalies, which have radii < 50km, are correlated with areas of reduced seismicity, several in regions such as Japan and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) trench-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the subduction zones analyzed. Despite great length along strike, these ridges are less than 100 km wide and several appear uncompensated. A high proportion of arc-normal structure and the truncation/morphological transition of trench-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and subducting plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined trench-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links

  16. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, William J.; Braile, Lawrence W.; Vonfrese, Ralph R. B.

    1987-01-01

    Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication.

  17. Local Earth's gravity field in view of fractal dimension

    NASA Astrophysics Data System (ADS)

    Mészárosová, Katarína; Minarechová, Zuzana; Janák, Juraj

    2013-04-01

    The poster presents the relative roughness of chosen characteristics of the Earth's gravity field in several small regions in area of Slovakia (e.g. free-air anomaly, Bouguer anomaly, gravity disturbance...) using the values of fractal dimension. In this approach, a three dimensional box counting method and the Hurst analysis method are applied to estimate the values of fractal dimensions. Then the computed fractal dimension values are used to compare all 3D models of all chosen characteristics.

  18. A priori noise and regularization in least squares collocation of gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jarmołowski, Wojciech

    2013-12-01

    The paper describes the estimation of covariance parameters in least squares collocation (LSC) by the cross-validation (CV) technique called leave-one-out (LOO). Two parameters of Gauss-Markov third order model (GM3) are estimated together with a priori noise standard deviation, which contributes significantly to the covariance matrix composed of the signal and noise. Numerical tests are performed using large set of Bouguer gravity anomalies located in the central part of the U.S. Around 103 000 gravity stations are available in the selected area. This dataset, together with regular grids generated from EGM2008 geopotential model, give an opportunity to work with various spatial resolutions of the data and heterogeneous variances of the signal and noise. This plays a crucial role in the numerical investigations, because the spatial resolution of the gravity data determines the number of gravity details that we may observe and model. This establishes a relation between the spatial resolution of the data and the resolution of the gravity field model. This relation is inspected in the article and compared to the regularization problem occurring frequently in data modeling. Artykuł opisuje estymację parametrów kowariancji w kolokacji najmniejszych kwadratów (LSC) przy pomocy techniki kroswalidacji nazywanej leave-one-out (LOO). Wyznaczane są dwa parametry modelu Gaussa-Markova trzeciego rzędu (GM3) wraz z odchyleniem standardowym szumu a priori, które ma znaczny wpływ na macierz kowariancji złożoną z sygnału i szumu. Testy numeryczne przeprowadzono na dużym zbiorze anomalii grawimetrycznych Bouguera z obszaru centralnej części USA. Obszar ten mieści około 103000 pomiarów grawimetrycznych. Dane te wraz z regularnymi siatkami wygenerowanymi z modelu geopotencjalnego EGM2008 pozwalają na pracę z różną rozdzielczością przestrzenną i różnymi wariancjami sygnału i szumu. Odgrywa to kluczową rolę w badaniach numerycznych, ponieważ rozdzielczo

  19. Global correlation of topographic heights and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Roufosse, M. C.

    1977-01-01

    The short wavelength features were obtained by subtracting a calculated 24th-degree-and-order field from observed data written in 1 deg x 1 deg squares. The correlation between the two residual fields was examined by a program of linear regression. When run on a worldwide scale over oceans and continents separately, the program did not exhibit any correlation; this can be explained by the fact that the worldwide autocorrelation function for residual gravity anomalies falls off much faster as a function of distance than does that for residual topographic heights. The situation was different when the program was used in restricted areas, of the order of 5 deg x 5 deg square. For 30% of the world,fair-to-good correlations were observed, mostly over continents. The slopes of the regression lines are proportional to apparent densities, which offer a large spectrum of values that are being interpreted in terms of features in the upper mantle consistent with available heat-flow, gravity, and seismic data.

  20. Gravity anomalies of the active mud diapirs off southwest Taiwan

    NASA Astrophysics Data System (ADS)

    Doo, Wen-Bin; Hsu, Shu-Kun; Lo, Chung-Liang; Chen, Song-Chuen; Tsai, Ching-Hui; Lin, Jing-Yi; Huang, Yuan-Ping; Huang, Yin-Sheng; Chiu, Shye-Donq; Ma, Yu-Fang

    2015-12-01

    Overpressure and buoyant effect of underlying sediments are generally used to account for the upward motion or formation of submarine mud volcanoes and mud diapirs. In this study, we process and interpret the gravity anomalies associated with the active mud diapirs off SW Taiwan. Geologically, the mud diapirs are just formed and are still very active, thus we can better understand the initial process of the mud diapirs formation through the gravity analysis. Our results show that the density contrasts of the submarine mud diapirs with respect to the surroundings are generally positive. Because the study area is in a tectonically compressive regime and the gas plume venting from the submarine mud volcanoes is very active, we thus infer that mechanically the mud diapirs off SW Taiwan have been formed mainly due to the tectonic compression on the underlying sediments of high pore-fluid pressure, instead of the buoyancy of the buried sediments. The overpressured sediments and fluid are compressed and pushed upwards to pierce the overlying sediments and form the more compacted mud diapirs. The relatively denser material of the mud diapirs probably constrains the flowing courses of the submarine canyons off SW Taiwan, especially for the upper reaches of the Kaoping and Fangliao submarine canyons.

  1. Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand

    SciTech Connect

    Hunt, T.M. )

    1992-04-01

    This paper discusses a re-examination of gravity which indicates that Rotorua Caldera does not have the circular, negative gravity anomaly typical of other rhyolitic calderas. New gravity measurements and residual gravity anomalies in Rotorua City are consistent with numerous rhyolite domes and ignimbrite sheets, interbedded with a thick sequence of poorly-compacted sediments. Within the city a gravity high extends from the shore of Lake Rotorua south to Whakarewarewa and is associated with a buried ridge, formed by the coalescing of two rhyolite domes. A gravity low centered near Linton Park suggests that rhyolites are thin or absent in this area and sediments extend to a depth of about 1 km. A quantitative analysis of the residual gravity anomalies was limited by insufficient information about the density, extent, and thickness of the material underlying the rhyolites, and the uncertainty in the distribution and density of silicification within the sediments.

  2. Gravity Anomalies in the Northern Hawaiian Islands: Evidence for an Alternative Magma Chamber on Kauai and a Conjoined Niihau-Kauai Island

    NASA Astrophysics Data System (ADS)

    Flinders, A. F.; Ito, G.; Garcia, M.; Kim, S.; Appelgate, B.

    2008-12-01

    The shield stage evolution of the islands of Kauai and Niihau are poorly understood. Previous land-based gravity surveys provide only a coarse constraint on the observed gravitational field. Questions as to whether the island of Kauai was formed by a single or multiple shields and the developmental relationship between these neighboring islands are still debated. Our new land-based gravity survey of Kauai and ship-board gravity surveys around both islands identified large complete Bouguer gravitational anomalies under Kauai's Lihue Basin and offshore in the Kaulakahi Channel, a 30-km-long bathymetric ridge connecting the two islands. These gravitational highs are consistent in size and magnitude with those of other Hawaiian islands and imply local zones of high density crust, most likely attributed to magmatic intrusions; e.g. former magma chambers, or rift zones. The Lihue Basin anomaly observed is offset 20 km east from the geologically mapped caldera region. This offset implies either the unlikely case that the shield stage plumbing system connecting the magma chamber and caldera could have been inclined by up to 75 degrees from the vertical, or that the currently mapped caldera is a late feature, unrelated to shield volcanism. The location of the gravitational anomaly, in the Kaulakahi Channel, 20 km east of Niihau is consistent with geologic mapping, which indicates that Niihau is a remnant of an ancient shield volcano centered east of the island. The proximity of the Niihau gravitational anomaly 10 km from the western edge of Kauai supports the hypothesis that the two volcanoes were part of the same island.

  3. The quest for the perfect gravity anomaly: Part 1 - New calculation standards

    USGS Publications Warehouse

    Li, X.; Hildenbrand, T.G.; Hinze, W. J.; Keller, Gordon R.; Ravat, D.; Webring, M.

    2006-01-01

    The North American gravity database together with databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revision of procedures and standards for calculating gravity anomalies taking into account our enhanced computational power, modern satellite-based positioning technology, improved terrain databases, and increased interest in more accurately defining different anomaly components. The most striking revision is the use of one single internationally accepted reference ellipsoid for the horizontal and vertical datums of gravity stations as well as for the computation of the theoretical gravity. The new standards hardly impact the interpretation of local anomalies, but do improve regional anomalies. Most importantly, such new standards can be consistently applied to gravity database compilations of nations, continents, and even the entire world. ?? 2005 Society of Exploration Geophysicists.

  4. An Anzatz about Gravity, Cosmology, and the Pioneer Anomaly

    SciTech Connect

    Murad, Paul

    2010-01-28

    The Pulsar 1913+16 binary system may represent a 'young' binary system where previously it is claimed that the dynamics are due to either a third body or a gravitational vortex. Usually a binary system's trajectory could reside in a single ellipse or circular orbit; the double ellipse implies that the 1913+16 system may be starting to degenerate into a single elliptical trajectory. This could be validated only after a considerably long time period. In a majority of binary star systems, the weights of both stars are claimed by analysis to be the same. It may be feasible that the trajectory of the primary spinning star could demonstrate repulsive gravitational effects where the neutron star's high spin rate induces a repulsive gravitational source term that compensates for inertia. If true, then it provides evidence that angular momentum may be translated into linear momentum as a repulsive source that has propulsion implications. This also suggests mass differences may dictate the neutron star's spin rate as an artifact of a natural gravitational process. Moreover, the reduced matter required by the 'dark' mass hypothesis may not exist but these effects could be due to repulsive gravity residing in rotating celestial bodies.The Pioneer anomaly observed on five different deep-space spacecraft, is the appearance of a constant gravitational force directed toward the sun. Pioneer spacecraft data reveals that a vortex-like magnetic field exists emanating from the sun. The spiral arms of the Sun's magnetic vortex field may be causal to this constant acceleration. This may profoundly provide a possible experimental verification on a cosmic scale of Gertsenshtein's principle relating gravity to electromagnetism. Furthermore, the anomalous acceleration may disappear once the spacecraft passes out into a magnetic spiral furrow, which is something that needs to be observed in the future. Other effects offer an explanation from space-time geometry to the Yarkovsky thermal

  5. High-resolution airborne gravity imaging over James Ross Island (West Antarctica)

    USGS Publications Warehouse

    Jordan, T.A.; Ferraccioli, F.; Jones, P.C.; Smellie, J.L.; Ghidella, M.; Corr, H. F. J.; Zakrajsek, A.F.

    2007-01-01

    James Ross Island (JRI) exposes a Miocene-Recent alkaline basaltic volcanic complex that developed in a back-arc, east of the northern Antarctic Peninsula. JRI has been the focus of several geological studies because it provides a window on Neogene magmatic processes and paleoenvironments. However, little is known about its internal structure. New airborne gravity data were collected as part of the first high-resolution aerogeophysical survey flown over the island and reveal a prominent negative Bouguer gravity anomaly over Mt Haddington. This is intriguing as basaltic volcanoes are typically associated with positive Bouguer anomalies, linked to underlying mafic intrusions. The negative Bouguer anomaly may be associated with a hitherto unrecognised low-density sub-surface body, such as a breccia-filled caldera, or a partially molten magma chamber.

  6. Crustal structure and gravity anomalies beneath the Rif, northern Morocco: implications for the current tectonics of the Alboran region

    NASA Astrophysics Data System (ADS)

    Petit, Carole; Le Pourhiet, Laetitia; Scalabrino, Bruno; Corsini, Michel; Bonnin, Mickaël; Romagny, Adrien

    2015-07-01

    We analyse Bouguer anomaly data and previously published Moho depths estimated from receiver functions in order to determine the amount of isostatic compensation or uncompensation of the Rif topography in northern Morocco. We use Moho depth variations extracted from receiver function analyses to predict synthetic Bouguer anomalies that are then compared to observed Bouguer anomaly. We find that Moho depth variations due to isostatic compensation of topographic and/or intracrustal loads do not match Moho depth estimates obtained from receiver function analyses. The isostatic misfit map evidences excess crustal root as large as 10 km in the western part of the study area, whereas a `missing' crustal root of ˜5 km appears east of 4.3°E. This excess root/missing topography correlates with the presence of a dense mantle lid, the noticeable southwestward drift of the Western Rif area, and with a current surface uplift. We propose that a delaminated mantle lid progressively detaching westward or southwestward from the overlying crust is responsible for viscous flow of the ductile lower crust beneath the Rif area. This gives rise to isostatic uplift and westward drift due to viscous coupling at the upper/lower crust boundary. At the same time, the presence of this dense sinking mantle lid causes a negative dynamic topography, which explains why the observed topography is too low compared to the crustal thickness.

  7. Procedures and results related to the direct determination of gravity anomalies from satellite and terrestrial gravity data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1974-01-01

    The equations needed for the incorporation of gravity anomalies as unknown parameters in an orbit determination program are described. These equations were implemented in the Geodyn computer program which was used to process optical satellite observations. The arc dependent parameter unknowns, 184 unknown 15 deg and coordinates of 7 tracking stations were considered. Up to 39 arcs (5 to 7 days) involving 10 different satellites, were processed. An anomaly solution from the satellite data and a combination solution with 15 deg terrestrial anomalies were made. The limited data samples indicate that the method works. The 15 deg anomalies from various solutions and the potential coefficients implied by the different solutions are reported.

  8. Classical geometrical interpretation of ghost fields and anomalies in Yang-Mills theory and quantum gravity

    SciTech Connect

    Thierry-Mieg, J.

    1985-05-14

    The reinterpretation of the BRS equations of Quantum Field Theory as the Maurer Cartan equation of a classical principal fiber bundle leads to a simple gauge invariant classification of the anomalies in Yang Mills theory and gravity.

  9. On the ratio of dynamic topography and gravity anomalies in a dynamic Earth

    NASA Astrophysics Data System (ADS)

    Colli, L.; Ghelichkhan, S.; Bunge, H.-P.

    2016-03-01

    Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free-air gravity anomalies (<30 mGal) associated with Earth's long-wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well-established formalism of global, self-gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half-space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal.

  10. Analysis of gravity anomaly over coral-reef oil field: Wilfred Pool, Sullivan County, Indiana

    SciTech Connect

    Dana, S.W.

    1980-03-01

    To compare the measured and theoretical gravity anomaly of a typical coral-reef oil field, data were collected from the wilfred Pool, Sullivan County, Indiana. Densities of available core samples from the field were determined and the anomaly was calculated, taking into account the lateral and vertical variation of density and the geologic structure known from core studies and drilling-log records of lithologic types penetrated by the wells. Comparison of the theoretical and actual anomalies indicated a rough correspondence except for several sharp negative anomalies on the flanks of the measured gravity anomaly. Further studies indicated that the negative anomalies are possibly due to fluvial erosion that produced, on the surface of the youngest Pennsylvanian sediments, channels which were later filled with glacial till of lower density than the sediments. 13 figures.

  11. Gravity anomalies, plate tectonics and the lateral growth of Precambrian North America

    NASA Technical Reports Server (NTRS)

    Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

    1988-01-01

    The widespread gravity coverage of North America provides a picture of the gross structural fabric of the continent via the trends of gravity anomalies. The structural picture so obtained reveals a mosaic of gravity trend domains, many of which correlate closely with structural provinces and orogenic terranes. The gravity trend map, interpreted in the light of plate-tectonic theory, thus provides a new perspective for examining the mode of assembly and growth of North America. Suture zones, palaeosubduction directions, and perhaps, contrasting tectonic histories may be identified using gravity patterns.

  12. Gravity data from the San Pedro River Basin, Cochise County, Arizona

    USGS Publications Warehouse

    Kennedy, Jeffrey R.; Winester, Daniel

    2011-01-01

    The U.S. Geological Survey, Arizona Water Science Center in cooperation with the National Oceanic and Atmospheric Administration, National Geodetic Survey has collected relative and absolute gravity data at 321 stations in the San Pedro River Basin of southeastern Arizona since 2000. Data are of three types: observed gravity values and associated free-air, simple Bouguer, and complete Bouguer anomaly values, useful for subsurface-density modeling; high-precision relative-gravity surveys repeated over time, useful for aquifer-storage-change monitoring; and absolute-gravity values, useful as base stations for relative-gravity surveys and for monitoring gravity change over time. The data are compiled, without interpretation, in three spreadsheet files. Gravity values, GPS locations, and driving directions for absolute-gravity base stations are presented as National Geodetic Survey site descriptions.

  13. Lithologic mapping test for gravity and magnetic anomalies. A case study of gravity-magnetic anomaly profile in the eastern segment of the China-Mongolia border

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Meng, Xiaohong; Chen, Zhaoxi; Liu, Guofeng; Zheng, Yuanman; Wang, Jun; Zhang, Sheng; Zhang, Xingdong; Zheng, Wanqiu

    2015-06-01

    An inversion calculation is usually needed to map lithologies with gravity-magnetic anomalies. A lithological-physical property correspondence can be established by combining data of regional rock density and magnetic susceptibility to build topological equations. In this study, topological calculations were performed using inversion data and combined with physical property data to interpret and map lithologies. Gravity-magnetic profiles from the eastern segment of the China-Mongolia border were used (Jining-Bainaimiao-Ha'ernaode geological-composite geophysical profile) in this paper. Based on gravity-magnetic anomaly inversion, the rock density and magnetic susceptibility data of Bainaimiao and Jining were adopted for lithological inversion. Distribution characteristics of four major types of magmatic rocks within 50 km of the lower half space were obtained, and results of lithologic mapping and tectonic framework were analyzed. The position of convergence between the North China Plate and Siberian Plate was confirmed. Two tectonic stages were identified, namely, interplate squeezing and intraplate deformation. Regional gravity-magnetic field properties were analyzed to discuss the orientation and date of andesites and diorites in the northern part of the survey line. We believe that they have a northeast-southwest orientation similar to gravity-magnetic anomalies of Erenhot-Xilinhot. They resemble the igneous rock near Erenhot because they both indicate magmatic intrusion during the early Carboniferous.

  14. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Vonfrese, R. R. B.

    1985-01-01

    Current limitations in the quantitative interpretation of satellite-elevation geopotential field data and magnetic anomaly data were investigated along with techniques to overcome them. A major result was the preparation of an improved scalar magnetic anomaly map of South America and adjacent marine areas directly from the original MAGSAT data. In addition, comparisons of South American and Euro-African data show a strong correlation of anomalies along the Atlantic rifted margins of the continents.

  15. Lithospheric structure across the central Tien Shan constrained by gravity anomalies and joint inversions of receiver function and Rayleigh wave dispersion

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Shi, Lei; Gao, Jiayi

    2016-07-01

    Shear wave velocity structure across the central Tien Shan orogeny was generated by jointly inverting Rayleigh wave phase and group velocity with teleseismic P-wave receiver functions at 40 broadband seismic stations. The inferred seismic structure was validated by forward modeling of the complete Bouguer anomaly data. The joint inversion result reveals larger crust thicknesses beneath the Kokshaal (∼68-72 km) and Kyrgyz ranges (∼62-64 km), while other units have crustal thicknesses between 48 and 58 km. A fast velocity layer (Vs = 3.6-3.9 km/s) in the upper crust is found in some seismic stations within the Kazakh Shield. Our models show the presence of high velocity and density layers in the lowermost crust throughout the region, consistent with the presence of mafic/ultramafic lithologies. The large crustal thickness is associated with a thickened mafic layer in the lower crust, indicating that the thickened crust may be partly caused by magmatic underplating. The low velocity and density anomaly in the middle crust, and low upper mantle velocity observed in our model beneath the middle Tien Shan reflect the presence of partial melt in the crust due to the intrusion of hot mantle material. The lack of correlation between Moho depth and topography, together with the gravity results, suggests that the topographic compensation in the central Tien Shan is not confined to the crust. This requires significant support from the mantle to account for the relative high elevation of the middle Tien Shan.

  16. Inversion of Oceanic Lithosphere Density Structure in the South China Sea by Satellite Gravity

    NASA Astrophysics Data System (ADS)

    Zhang, S.

    2013-12-01

    In this paper, the satellite altimetry gravity anomaly is used to calculate the Bouguer gravity by Seafloor terrain correction in the South China Sea. The faults distribution and basin boundary is extracted to study the geological structure unit. The 3D density inversion method is applied to invert the oceanic lithosphere density structure. In the 3D density inversion method, the depth weighting function is an experience function derived by the relation between gravity anomaly and depth. It is difficult to artificially choose reasonable values of the weighting factors which have great effect on the inversion result. The power spectrum of the gravity anomaly is used to estimate the depth of the geological body, and the function of the weighting factors and the gravity anomaly is built. The weighting factors can be estimated automatically by the gravity anomaly power spectrum. Therefore, the artificial error can be avoided and the accuracy of inversion is improved. In the density inversion, the Bouguer gravity is firstly decomposed into different scales by wavelet transform method. The gravity anomaly in different scales is related to the density distribution in different depth. Then, the power spectrum is calculated by gravity anomaly in different scales to estimate the weighting factors. Finally, the ocean lithosphere density structure in the South China Sea is inverted and compared with its velocity structure.

  17. Relation of the lunar volcano complexes lying on the identical linear gravity anomaly

    NASA Astrophysics Data System (ADS)

    Yamamoto, K.; Haruyama, J.; Ohtake, M.; Iwata, T.; Ishihara, Y.

    2015-12-01

    There are several large-scale volcanic complexes, e.g., Marius Hills, Aristarchus Plateau, Rumker Hills, and Flamsteed area in western Oceanus Procellarum of the lunar nearside. For better understanding of the lunar thermal history, it is important to study these areas intensively. The magmatisms and volcanic eruption mechanisms of these volcanic complexes have been discussed from geophysical and geochemical perspectives using data sets acquired by lunar explorers. In these data sets, precise gravity field data obtained by Gravity Recovery and Interior Laboratory (GRAIL) gives information on mass anomalies below the lunar surface, and useful to estimate location and mass of the embedded magmas. Using GRAIL data, Andrews-Hanna et al. (2014) prepared gravity gradient map of the Moon. They discussed the origin of the quasi-rectangular pattern of narrow linear gravity gradient anomalies located along the border of Oceanus Procellarum and suggested that the underlying dikes played important roles in magma plumbing system. In the gravity gradient map, we found that there are also several small linear gravity gradient anomaly patterns in the inside of the large quasi-rectangular pattern, and that one of the linear anomalies runs through multiple gravity anomalies in the vicinity of Aristarchus, Marius and Flamstead volcano complexes. Our concern is whether the volcanisms of these complexes are caused by common factors or not. To clarify this, we firstly estimated the mass and depth of the embedded magmas as well as the directions of the linear gravity anomalies. The results were interpreted by comparing with the chronological and KREEP distribution maps on the lunar surface. We suggested providing mechanisms of the magma to these regions and finally discussed whether the volcanisms of these multiple volcano complex regions are related with each other or not.

  18. Long-wavelength Magnetic and Gravity Anomaly Correlations of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J. (Principal Investigator); Olivier, R.

    1984-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic Shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  19. Long-wavelength magnetic and gravity anomaly correlations on Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Olivier, R.; Hinze, W. J.

    1985-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  20. Global accuracy estimates of point and mean undulation differences obtained from gravity disturbances, gravity anomalies and potential coefficients

    NASA Technical Reports Server (NTRS)

    Jekeli, C.

    1979-01-01

    Through the method of truncation functions, the oceanic geoid undulation is divided into two constituents: an inner zone contribution expressed as an integral of surface gravity disturbances over a spherical cap; and an outer zone contribution derived from a finite set of potential harmonic coefficients. Global, average error estimates are formulated for undulation differences, thereby providing accuracies for a relative geoid. The error analysis focuses on the outer zone contribution for which the potential coefficient errors are modeled. The method of computing undulations based on gravity disturbance data for the inner zone is compared to the similar, conventional method which presupposes gravity anomaly data within this zone.

  1. GEOS 3 data processing for the recovery of geoid undulations and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The paper discusses the analysis of GEOS 3 altimeter data for the determination of geoid heights and point and mean gravity anomalies. Methods are presented for determining the mean anomalies and mean undulations from the GEOS 3 altimeter data available by the end of September 1977 without having a complete set of precise orbits. The editing of the data is extensive to remove questionable data, although no filtering of the data is carried out. An adjustment process is carried out to eliminate orbit error and altimeter bias. Representative point anomaly values are computed to investigate anomaly behavior across the Bonin Trench and over the Patton seamounts.

  2. Mantle origin of the Emeishan large igneous province from an analysis of residual gravity anomalies

    NASA Astrophysics Data System (ADS)

    Deng, Y.; Zhang, Z.; Mooney, W. D.; Fan, W.; Zhong, Q.; Badal, J.

    2013-12-01

    The Emeishan large igneous province (ELIP) is the only verified large igneous province in China. It covers an area of 250,000 km2 from the eastern margin of the Tibetan Plateau to the western margin of the Yangtze block. Most studies on ELIP are from geochemistry and tectonics, but the deep origin of the ELIP is still unclear. In this study, we investigate the residual gravity anomaly in South China and its relationship to the Emeishan large igneous province with constrains of lithospheric structure from deep seismic sounding profiles, deep seismic reflection surveys, and a variety of broadband seismic observations acquired in South China in the last several decades. Our working scheme consists of removing the respective gravitational effects due to: (1) the sediments, and undulations of the (2) crystalline basement, (3) upper crust; (4) Moho and (5) lithospheric thickness. We have thus obtained the residual gravity anomaly of the ELIP and surrounding region, striking positive residual anomaly with maximum value of 140 mGal is observed at the ELIP region. We use the conjugate gradient method to locate the deep origins of the residual gravity data. As a result, our preferred model consists of a positive cylindrical density anomaly that provides a fit to the residual gravity anomaly observed in ELIP. As the distance increases from the inner zone of the ELIP to the outer zone, the positive residual gravity decreases. Hence, in our model, the density anomaly decreases from about 0.06 g/cm3 beneath the inner zone to about 0.03 g/cm3 beneath the outer zone. The residual gravity and our preferred density anomaly provide new evidence, along with the seismic data and geochemical data, to confirm the domal structure of the Permian mantle plume that gave rise to the Emenshan Large Igneous Province.

  3. Investigation of urban faults in Shenzhen using wavelet multi-scale analysis and modeling of gravity observations

    NASA Astrophysics Data System (ADS)

    Xu, Chuang; Chen, Liang; Liu, Xi-kai

    2016-04-01

    Urban faults in Shenzhen are potential threat to the city security and sustainable development. To improve the knowledge of the Shenzhen fault zone, interpretation and inversion of gravity data were carried out. Bouguer gravity covering the whole Shenzhen city was calculated with a resolution of 1kmx1km. Wavelet multi-scale analysis (MSA) was applied to the Bouguer gravity data to obtain the multilayer residual anomalies corresponding to different depths. In addition, 2D gravity models were constructed along three profiles. The Bouguer gravity anomaly shows a NE-striking high-low-high pattern from northwest to southeast, strongly related to the main faults. According to the result of MSA, the correlation between gravity anomaly and faults is particularly significant from 4 to 12 km depth. The residual gravity with small amplitude in each layer indicates weak tectonic activity in the crust. In the upper layers, positive anomalies along most of faults reveal the upwelling of high-density materials during the past tectonic movements. The multilayer residual anomalies also implicate important information about the faults, such as the vertical extension and the dip direction. The maximum depth of the faults is about 20km. In general, NE-striking faults extend deeper than NW-striking Faults and have a larger dip angle. This study is supported by the National Natural Science Foundation of China (Grant No.41504015) and China Postdoctoral Science Foundation (Grant No.2015M572146).

  4. Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition

    NASA Astrophysics Data System (ADS)

    Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing

    2015-09-01

    In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.

  5. South China Sea crustal thickness and lithosphere thinning from satellite gravity inversion incorporating a lithospheric thermal gravity anomaly correction

    NASA Astrophysics Data System (ADS)

    Kusznir, Nick; Gozzard, Simon; Alvey, Andy

    2016-04-01

    The distribution of ocean crust and lithosphere within the South China Sea (SCS) are controversial. Sea-floor spreading re-orientation and ridge jumps during the Oligocene-Miocene formation of the South China Sea led to the present complex distribution of oceanic crust, thinned continental crust, micro-continents and volcanic ridges. We determine Moho depth, crustal thickness and continental lithosphere thinning (1- 1/beta) for the South China Sea using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir, 2008). The gravity inversion method provides a prediction of ocean-continent transition structure and continent-ocean boundary location which is independent of ocean isochron information. A correction is required for the lithosphere thermal gravity anomaly in order to determine Moho depth accurately from gravity inversion; the elevated lithosphere geotherm of the young oceanic and rifted continental margin lithosphere of the South China Sea produces a large lithosphere thermal gravity anomaly which in places exceeds -150 mGal. The gravity anomaly inversion is carried out in the 3D spectral domain (using Parker 1972) to determine 3D Moho geometry and invokes Smith's uniqueness theorem. The gravity anomaly contribution from sediments assumes a compaction controlled sediment density increase with depth. The gravity inversion includes a parameterization of the decompression melting model of White & McKenzie (1999) to predict volcanic addition generated during continental breakup lithosphere thinning and seafloor spreading. Public domain free air gravity anomaly, bathymetry and sediment thickness data are used in this gravity inversion. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy, rift orientation and sea-floor spreading trajectory. SCS conjugate margins

  6. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Leftwich, John; Nowroozi, Ali, A.

    1999-10-01

    This work reports the progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one-degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  7. Gravity investigation of the Manson impact structure, Iowa

    NASA Technical Reports Server (NTRS)

    Plescia, J. B.

    1993-01-01

    The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater

  8. Gravity investigation of the Manson impact structure, Iowa

    NASA Astrophysics Data System (ADS)

    Plescia, J. B.

    1993-03-01

    The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater

  9. Gravity anomalies of irregularly shaped two-dimensional bodies with constant horizontal density gradient

    USGS Publications Warehouse

    Pan, Jeng-Jong

    1989-01-01

    An equation to compute the gravity anomalies of two-dimensional (2-D) bodies with density contrast varying with depth (z axis) was developed by Murthy and Rao (1979). I develop an equation for computing the gravity anomalies of 2-D bodies with constant horizontal density gradient. By combining this equation with the equation of Murthy and Rao, I estimate the depth of the sedimentary basin which is adjacent to the master fault associated with the Rio Grande rift in New Mexico, where the density is assumed to decrease basinward from the fault (Cordell, 1979).

  10. Plumes in the mantle. [free air and isostatic gravity anomalies for geophysical interpretation

    NASA Technical Reports Server (NTRS)

    Khan, M. A.

    1973-01-01

    Free air and isostatic gravity anomalies for the purposes of geophysical interpretation are presented. Evidence for the existance of hotspots in the mantle is reviewed. The prosposed locations of these hotspots are not always associated with positive gravity anomalies. Theoretical analysis based on simplified flow models for the plumes indicates that unless the frictional viscosities are several orders of magnitude smaller than the present estimates of mantle viscosity or alternately, the vertical flows are reduced by about two orders of magnitude, the plume flow will generate implausibly high temperatures.

  11. On the recovery of gravity anomalies from high precision altimeter data

    NASA Technical Reports Server (NTRS)

    Lelgemann, D.

    1976-01-01

    A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

  12. Mafic and ultramafic rocks of the northwestern Brooks Range of Alaska produce nearly symmetric gravity anomalies

    SciTech Connect

    Morin, R.L. )

    1993-04-01

    An arc of mafic and ultramafic rocks is mapped from Asik Mountain to Siniktanneyak Mountain in the northwestern Brooks Range of Alaska. Gravity data, although not very detailed, have been collected over the region and show some very conspicuous circular or oval gravity highs over portions of the mapped mafic-ultramafic bodies. Bodies which have large associated gravity anomalies are Asik Mountain (80 mGal), Avon Hills (20 mGal), Misheguk Mountain (30 mGal), and Siniktanneyak Mountain (20 mGal). Gabbros of the Siniktanneyak Mountain complex, where the gravity coverage is best, have densities of about 3.0 g/cm[sup 3] while the densities of the surrounding sedimentary rocks are about 2.6 g/cm[sup 3]. Volcanic rocks in the area have average densities of about 2.7 g/cm[sup 3]. Three-dimensional modeling indicates that the largest anomaly, on the southwestern part of the complex, could be caused by a polygonal prism of gabbro with vertical sides, about 6 km across and about 4.5 km deep. A smaller lobe of the anomaly on the northeast of the complex could be caused by another oblong polygonal prism about 4 km long and 2 km wide trending northeast and about 1.5 km deep. Modeling this anomaly with densities lower than gabbro would require greater thicknesses to produce the same anomaly. Modeling each anomaly along this arc in 2 1/2-dimensions shows many possible solutions using different body shapes and different density contrasts. There are several other gravity anomalies in this vicinity which could represent unexposed high density rocks. One such anomaly is in the Maiyumerak Mountains northeast of Asik Mountain (30 mGal). Another anomaly is to the northwest of Asik Mountain (20 mGal). There is also an anomaly at Uchugrak (20 mGal) east of Avan Hills. Although many of the anomalies in this region are poorly controlled, an attempt has been made to interpret the data to show possible solutions.

  13. Using Grail Data to Assess the Effect of Porosity and Dilatancy on the Gravity Signature of Impact Craters on the Moon

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, J., IV; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Zuber, M. T.

    2014-12-01

    NASA's dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution; this has enabled the study of craters of all sizes and ages. Soderblom et al. [2014, LPSC abstract #1777] calculated the residual Bouguer anomalies for ~2700 craters 27-184 km in diameter (D). They found that the residual Bouguer anomaly over craters smaller than D~100 km is essentially 0±50 mGal, there is a transition for D~100-150 km, and craters larger than 184 km have a positive residual Bouguer anomaly that increases with increasing crater size. We use the iSALE shock physics hydrocode to model crater formation, including the effect of porosity and dilatancy (shear bulking). We use strength parameters of gabbroic anorthosite for the crust and dunite for the mantle. Our impactor sizes range from 6-30 km, which produce craters between 86-450 km in diameter for pre-impact target porosities of 0, 6.8, and 13.6%. We calculate the free-air and Bouguer gravity anomalies from our models and compare them to gravity data from GRAIL. We find that target porosity has the greatest effect on the gravity signature of lunar craters and can explain the observed ±50 mGal scatter in the residual Bouguer anomaly. We investigate variations of impact velocity, crustal thickness, and dilatancy angle; we find that these parameters do not affect the gravity as significantly as target porosity does. We find that the crater diameter at which mantle uplift dominates the crater gravity is dependent on target porosity, and that it occurs at a crater diameter that is close to the complex crater to peak-ring basin transition.

  14. Kerr metric, geodesic motion, and Flyby Anomaly in fourth-order Conformal Gravity

    NASA Astrophysics Data System (ADS)

    Varieschi, Gabriele U.

    2014-06-01

    In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity (GR). Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard GR Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton-Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion—similar to Carter's constant—can also be introduced in Conformal Gravity. Consequently, we derive the fundamental equations of geodesic motion and show that the problem of solving these equations can be reduced to one of quadratures. In particular, we study the resulting time-like geodesics in Conformal Gravity Kerr geometry by numerically integrating the equations of motion for Earth flyby trajectories of spacecraft. We then compare our results with the existing data of the Flyby Anomaly in order to ascertain whether Conformal Gravity corrections are possibly the origin of this gravitational anomaly. Although Conformal Gravity slightly affects the trajectories of geodesic motion around a rotating spherical object, we show that these corrections are minimal and are not expected to be the origin of the Flyby Anomaly, unless conformal parameters are drastically different from current estimates. Therefore, our results confirm previous analyses, showing that modifications due to Conformal Gravity are not likely to be detected at the Solar System level, but might affect gravity at the galactic or cosmological scale.

  15. Spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1981-01-01

    To facilitate geologic interpretation of satellite elevation potential field data, analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation. A powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion. Linear transformations of the equivalent source field lead to corresponding geoidal anomalies, pseudo-anomalies, vector anomaly components, spatial derivatives, continuations, and differential magnetic pole reductions. A number of examples using 1 deg-averaged surface free-air gravity anomalies of POGO satellite magnetometer data for the United States, Mexico, and Central America illustrate the capabilities of the method.

  16. Analyzing and modeling gravity and magnetic anomalies using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    Computer codes were completed, tested, and documented for analyzing magnetic anomaly vector components by equivalent point dipole inversion. The codes are intended for use in inverting the magnetic anomaly due to a spherical prism in a horizontal geomagnetic field and for recomputing the anomaly in a vertical geomagnetic field. Modeling of potential fields at satellite elevations that are derived from three dimensional sources by program SPHERE was made significantly more efficient by improving the input routines. A preliminary model of the Andean subduction zone was used to compute the anomaly at satellite elevations using both actual geomagnetic parameters and vertical polarization. Program SPHERE is also being used to calculate satellite level magnetic and gravity anomalies from the Amazon River Aulacogen.

  17. Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

    NASA Technical Reports Server (NTRS)

    Bowin, C.

    1982-01-01

    A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

  18. Gravity anomalies of the Northern Hawaiian Islands: Implications on the shield evolutions of Kauai and Niihau

    NASA Astrophysics Data System (ADS)

    Flinders, Ashton F.; Ito, Garrett; Garcia, Michael O.

    2010-08-01

    New land and marine gravity data reveal two positive residual gravity anomalies in the Northern Hawaiian Islands: one over Kaua'i, the other between the islands of Kaua'i and Ni'ihau. These gravitational highs are similar in size and magnitude to those of other Hawaiian volcanoes, indicating local zones of high-density crust, attributed to olivine cumulates in solidified magma reservoirs. The residual gravity high over Kaua'i is located in the Līhu'e Basin, offset 8-12 km east of Kaua'i's geologically mapped caldera. This offset suggests that the mapped caldera is a collapsed feature later filled in with lava and not the long-term center of Kaua'i shield volcanism. A second residual gravity high, in the submarine channel between Kaua'i and Ni'ihau, marks the volcanic center of the Ni'ihau shield volcano. This second residual gravity anomaly implies that Ni'ihau's eastern boundary extended ˜20 km east of its present location. Through inversion, the residual gravity anomalies were modeled as being produced by two solidified magma reservoirs with average densities of 3100 kg/m3 and volumes between 2470 and 2540 km3. Considering the locations and sizes of the residual gravity anomalies/magma reservoirs, the extent of the two islands' paleoshorelines and potassium-argon dating of shield-stage lavas, we conclude that the two islands were not connected subaerially during their respective shield stages and that Ni'ihau's topographic summit was removed by an eastern flank collapse between 4.3 and 5.6 Ma. Continued constructional volcanism on western Kaua'i likely covered much of the submerged remains of eastern Ni'ihau.

  19. Direct recovery of mean gravity anomalies from satellite to satellite tracking

    NASA Technical Reports Server (NTRS)

    Hajela, D. P.

    1974-01-01

    The direct recovery was investigated of mean gravity anomalies from summed range rate observations, the signal path being ground station to a geosynchronous relay satellite to a close satellite significantly perturbed by the short wave features of the earth's gravitational field. To ensure realistic observations, these were simulated with the nominal orbital elements for the relay satellite corresponding to ATS-6, and for two different close satellites (one at about 250 km height, and the other at about 900 km height) corresponding to the nominal values for GEOS-C. The earth's gravitational field was represented by a reference set of potential coefficients up to degree and order 12, considered as known values, and by residual gravity anomalies obtained by subtracting the anomalies, implied by the potential coefficients, from their terrestrial estimates. It was found that gravity anomalies could be recovered from strong signal without using any a-priori terrestrial information, i.e. considering their initial values as zero and also assigning them a zero weight matrix. While recovering them from weak signal, it was necessary to use the a-priori estimate of the standard deviation of the anomalies to form their a-priori diagonal weight matrix.

  20. Gravity anomalies, crustal structure and flexure of the lithosphere at the Baltimore Canyon Trough

    NASA Astrophysics Data System (ADS)

    Watts, A. B.

    1988-07-01

    Seismic and gravity anomaly data have been used to examine the long-term mechanical properties of the lithosphere beneath the Baltimore Canyon Trough, a 15 km deep sedimentary basin in the rifted U.S. Atlantic margin. Seismic data constrain the crustal structure at the time of rifting as well as the amount of sedimentation and erosion that has occurred. The gravity effect of the initial crustal structure, sedimentary loading and erosional unloading have been computed and compared to the observed free-air gravity anomaly. The best fitting model is one in which the elastic thickness of the lithosphere ( Te) changes at the East Coast magnetic anomaly. Landward of the anomaly, Te is significantly smaller than previously reported values for continental or oceanic lithosphere of the same thermal age. Seaward of the anomaly, however, Te follows the depth to the 450°C oceanic isotherm which also describes the response of oceanic lithosphere to seamount and oceanic island loads. These results are interpreted as indicating that the shelf part of the trough is underlain by continental lithosphere which, following rifting, did not acquire any significant long-term strength.

  1. Principal facts of gravity stations with gravity and magnetic profiles from the Southwest Nevada Test Site, Nye County, Nevada, as of January, 1982

    USGS Publications Warehouse

    Jansma, P.E.; Snyder, D.B.; Ponce, David A.

    1983-01-01

    Three gravity profiles and principal facts of 2,604 gravity stations in the southwest quadrant of the Nevada Test Site are documented in this data report. The residual gravity profiles show the gravity measurements and the smoothed curves derived from these points that were used in geophysical interpretations. The principal facts include station label, latitude, longitude, elevation, observed gravity value, and terrain correction for each station as well as the derived complete Bouguer and isostatic anomalies, reduced at 2.67 g/cm 3. Accuracy codes, where available, further document the data.

  2. Crustal Thickness and Oceanic Lithosphere Distribution in the Eastern Mediterranean from Satellite Gravity Anomaly Inversion

    NASA Astrophysics Data System (ADS)

    Cowie, L.; Kusznir, N. J.

    2010-12-01

    The distribution of oceanic and continental lithosphere in the eastern Mediterranean is not well understood. Gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to map Moho depth, crustal thickness and continental lithosphere thinning factor for the eastern Mediterranean in order to determine the distribution of oceanic and continental lithosphere and the ocean-continent transition location. Data used in the gravity inversion are bathymetry, free-air gravity and sediment thickness data from Smith and Sandwell (1997), Sandwell and Smith (2009) and Laske and Masters (1997) respectively. Moho depths from the gravity inversion are dependent on the age of oceanic lithosphere and continental breakup because of the lithosphere thermal gravity correction; however, these ages are uncertain for the eastern Mediterranean. Gravity inversion sensitivities to break-up ages of 225Ma (late Triassic) and 100Ma (early Cretaceous) have been examined. Gravity inversion results show thin crust (5 - 10km thickness) for the Ionian Sea and the Herodotus Basin of the eastern Mediterranean consistent with these basins being underlain by oceanic or highly thinned continental crust. Predicted Moho depths from the gravity inversion are in agreement with published Ionian Sea ESP results (Voogd et al, 1992) and suggest a gravity inversion reference Moho depth increasing to the north, which we attribute to subduction dynamic subsidence. Calibration of gravity inversion Moho against ESP results show a trade-off between break-up age and reference Moho depth; a Cretaceous age ocean requires a larger Moho reference depth than a Triassic age ocean. Lithosphere thinning factor maps from gravity inversion for Africa do not show continuity between the Cretaceous African rift system (Benue Trough, Chad, CASZ and Sudan basins) and eastern Mediterranean basins. If the Ionian Sea is of Cretaceous age then it more probably links to Cretaceous rifting and sea

  3. 3D Inversion of Gravity Anomalies for the Interpretation of Sedimentary Basins using Variable Density Contrast

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Ertekin, Can

    2015-04-01

    Concern about sedimentary basins is generally related to their genetic and economic significance. Analysis of sedimentary basins requires the acquisition of data through outcrop studies and subsurface investigations that encompass drilling and geophysics. These data are commonly analysed by computer-assisted techniques. One of these methods is based on analysing gravity anomalies to compute the depth of sedimentary basin-basement rock interface. Sedimentary basins produce negative gravity anomalies, because they have mostly lower densities than that of the surrounding basement rocks. Density variations in a sedimentary fill increase rapidly at shallower depths then gradually reach the density of surrounding basement rocks due to the geostatic pressure i.e. compaction. The decrease of the density contrast can be easily estimated by a quadratic function. Hence, if the densities are chosen properly and the regional background is removed correctly, the topographical relief of the sedimentary basin-basement rock interface might be estimated by the inversion of the gravity data using an exponential density-depth relation. Three dimensional forward modelling procedure can be carried out by introducing a Cartesian coordinate system, and placing vertical prisms just below observation points on the grid plane. Depth to the basement, namely depths to the bottom of the vertical prisms are adjusted in an iterative manner by minimizing the differences between measured and calculated residual gravity anomalies. In this study, we present a MATLAB-based inversion code for the interpretation of sedimentary basins by approximating the topographical relief of sedimentary basin-basement rock interfaces. For a given gridded residual gravity anomaly map, the procedure estimates the bottom depths of vertical prisms by considering some published formulas and assumptions. The utility of the developed inversion code was successfully tested on theoretically produced gridded gravity data set

  4. Covariant anomaly and Hawking radiation from the modified black hole in the rainbow gravity theory

    NASA Astrophysics Data System (ADS)

    Peng, Jun-Jin; Wu, Shuang-Qing

    2008-12-01

    Recently, Banerjee and Kulkarni (R. Banerjee, S. Kulkarni, arXiv: 0707. 2449 [hep-th]) suggested that it is conceptually clean and economical to use only the covariant anomaly to derive Hawking radiation from a black hole. Based upon this simplified formalism, we apply the covariant anomaly cancellation method to investigate Hawking radiation from a modified Schwarzschild black hole in the theory of rainbow gravity. Hawking temperature of the gravity’s rainbow black hole is derived from the energy-momentum flux by requiring it to cancel the covariant gravitational anomaly at the horizon. We stress that this temperature is exactly the same as that calculated by the method of cancelling the consistent anomaly.

  5. Deconstructing the shallow internal structure of the Moon using GRAIL gravity and LOLA topography

    NASA Astrophysics Data System (ADS)

    Zuber, M. T.

    2015-12-01

    Globally-distributed, high-resolution gravity and topography observations of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission and Lunar Orbiter Laser Altimeter (LOLA) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft afford the unprecedented opportunity to explore the shallow internal structure of the Moon. Gravity and topography can be combined to produce Bouguer gravity that reveals the distribution of mass in the subsurface, with high degrees in the spherical harmonic expansion of the Bouguer anomalies sensitive to shallowest structure. For isolated regions of the lunar highlands and several basins we have deconstructed the gravity field and mapped the subsurface distribution of density anomalies. While specified spherical harmonic degree ranges can be used to estimate contributions at different depths, such analyses require considerable caution in interpretation. A comparison of filtered Bouguer gravity with forward models of disk masses with plausible densities illustrates the interdependencies of the gravitational power of density anomalies with depth and spatial scale. The results have implications regarding the limits of interpretation of lunar subsurface structure.

  6. Oceanwide gravity anomalies from Geos-3, Seasat and Geosat altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.; Basic, Tomislav

    1992-01-01

    Three kinds of satellite altimeter data have been combined, along with 5 x 5 arcmin bathymetric data, to calculate a 0.125 deg ocean wide gridded set of 2.3 x 10 exp 6 free-air gravity anomalies. The procedure used was least squares collocation that yields the predicted anomaly and standard deviation. The value of including the bathymetric data was shown in a test around the Dowd Seamount where the root mean square (rms) difference between ship gravity measurements decreased from +/- 40 mgal to +/- 20 mgal when the bathymetry was included. Comparisons between the predicted anomalies and ship gravity data is described in three cases. In the Banda Sea the rms differences were +/- 20 mgal for two lines. In the South Atlantic rms differences over lines of 2000 km in length were +/- 7 mgal. For cruise data in the Antarctica region the discrepancies were +/- 12 mgal. Comparisons of anomalies derived from the Geosat geodetic mission data by Marks and McAdoo (1992) with ship dta gave differences of +/- 6 mgal showing the value of the much denser Geosat geodetic mission altimeter data.

  7. Lithospheric structure across the central Tien Shan constrained by gravity anomalies and joint inversions of receiver function and Rayleigh group velocity data

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Shi, Lei; Gao, Jiayi

    2016-04-01

    Shear wave velocity structure across the central Tien Shan orogeny was generated by jointly inverting Rayleigh wave phase and group velocity with teleseismic P-wave receiver functions at 40 broad band seismic stations of the MANAS project. The inferred seismic structure was validated by forward modeling of the complete Bouguer anomaly data. The joint inversion result reveals larger crust thicknesses beneath the Kokshaal (~68-72 km) and Kyrgyz ranges (~62-64 km), while other units have crustal thicknesses between 48 and 58 km. A fast velocity layer (Vs = 3.6-3.9 km/s) in the upper crust is found in some seismic stations within the Kazakh Shield. Our models show the presence of high velocity and density layers in the lowermost crust throughout the region, consistent with the presence of mafic/ultramafic lithologies. The large crustal thickness is associated with a thickened mafic layer in the lower crust, indicating that the thickened crust may be partly caused by magmatic underplating. The low velocity and density anomaly in the middle crust, and low upper mantle velocity observed in our model beneath the middle Tien Shan reflects the presence of partial melt in the crust due to the intrusion of hot mantle material. The lack of correlation between Moho depth and topography, together with the gravity results, suggests that the topographic compensation in the central Tien Shan is not confined to the crust. This requires significant support from the mantle to account for the relative high elevation of the middle Tien Shan.

  8. Negative gravity anomaly over spreading rift valleys: Mid-Atlantic Ridge at 26°N

    NASA Astrophysics Data System (ADS)

    Bowin, Carl; Milligan, Julie

    1985-03-01

    A pronounced negative free-air gravity anomaly commonly occurs over the median valley of slow spreading ocean ridges. Previous results, using Wiener filtering and cross-spectral analysis techniques for the Mid-Atlantic Ridge, obtained estimates of the elastic plate thickness in the range of 7-13 km and the existence of a residual negative gravity anomaly over the median rift valley, suggesting that the rift valley has a response function different than the remainder of the spreading ridge. In this paper we have improved the derivation of the topography-gravity admittance function for spreading ocean crust by carefully avoiding several sources of spectral splattering when processing the data: (1) selecting data from a cruise that followed a flowline of central North Atlantic relative plate motion and hence is least corrupted by fracture zones; and (2) accounting for the difference in distance between the gravity meter and the regional variation in elevation as the ridge crest is traversed. Improvements of lesser importance include the use of cubic splines to interpolate to equally spaced data rather than linear interpolation, and correction of the free-air anomaly values for long-wavelength variations of the indirect effect. Comparison of the resulting admittance function to elastic flexure response functions suggests an elastic plate thickness of about 8 km. The improved admittance function, when convolved with the ridge topography, provides a predicted gravity profile that accounts very well for the negative anomaly over the rift valley. Therefore, the isostatic response function for the rift valley is similar to that for the topography away from the rift valley.

  9. Application of Magsat lithospheric modeling in South America. Part 1: Processing and interpretation of magnetic and gravity anomaly data

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (Principal Investigator); Keller, G. R.; Lidiak, E. G.

    1984-01-01

    Scalar magnetic anomaly data from MAGSAT, reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of South America and the Caribbean are compared to major crustal features. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative anomalies. Spherical earth magnetic modeling of the Amazon River and Takatu aulacogens in northeastern South America indicates a less magnetic crust associated with the aulacogens. Spherical earth modeling of both positive gravity and negative magnetic anomalies observed over the Mississippi Embayment indicate the presence of a nonmagnetic zone of high density material within the lower crust associated with the aulacogen. The MAGSAT scalar magnetic anomaly data and available free air gravity anomalies over Euro-Africa indicate several similar relationships.

  10. Preliminary Investigation of EarthScope EARS Derived MOHO Topography and Large Scale Faye Gravity Anomaly

    NASA Astrophysics Data System (ADS)

    Crain, K.; Holland, A. A.

    2013-12-01

    This is a preliminary investigation using the EarthScope EARS receiver functions in combination with the Faye gravity anomaly. This includes both qualitative and quantitative comparison of the large scale Faye anomaly with an expected 3D geology interpretation for the southern mid-continent U.S.A. The 3D geology interpretation consists of expected 3D topographies based on National Elevation Data, published formation elevations, measured and published basement topography with geology, and the expected MOHO topography calculated using the EARS estimated crustal thickness. The EARS automated receiver functions provides a large data set of automatically generated receiver functions and models of bulk crustal properties. These bulk crustal properties include crustal thickness, and Vp/Vs given an assumed Vp. The results from this automatic determination can be evaluated through the H-K stacking, and are often a good method to identify where there may be complex structure or poor quality data. Some a priori information is used to constrain the EARS crustal model. The observed Faye gravity anomaly is calculated using the observed gravity value at their observation location from the PACES gravity database and their extracted elevation from the national elevation data set. Then the expected Faye gravity is modeled using the expected 3D geology interpretation. The observed and modeled Faye gravity, along with the expected 3D geologic interpretation with its topographies and geology and their expected uncertainties are used in a simple 3D density inversion to evaluate the consistency of the estimated with the expected crust / MOHO interface. Areas with complex crustal geology and or inconsistent EARS data are identified as areas of higher uncertainty and require further study. Even areas with agreement between the expected MOHO topography and the Faye anomaly have interesting geology implications. For example: in central Oklahoma the 14 km deep Anadarko basin has a positive

  11. Preparation of Residual Gravity Maps for the Southern Cascade Mountains, Washington Using Fourier Analysis

    SciTech Connect

    Dishberger, Debra McLean

    1983-04-01

    This report represents a continuation of gravity work in the Cascade Mountains of Washington supported by the Division of Geology and Earth Resources since 1974. The purpose of this research has been collection of baseline gravity data for use in geothermal resource evaluation. Results of the Division's gravity studies to date are given in Danes and Phillips (1983a, 1983b). One of the problems encountered when analyzing gravity data is distinguishing between those parts of the data that represent geologic structures of interest, and those that do not. In many cases, the features of interest are relatively small, near-surface features, such as those sought in mineral, petroleum, or geothermal exploration. Gravity anomalies caused by such structures may be distorted or masked by anomalies caused by larger, deeper geologic structures. Gravity anomalies caused by relatively shallow, small geologic structures are termed residual anomalies. Those due to broad, deep-seated features can be described as regional anomalies. The purpose of this report is to describe a Fourier analysis method for separating residual and regional gravity anomalies from a complete Bouguer gravity anomaly field. The technique has been applied to gravity data from the Southern Cascade Mountains, Washington. Residual gravity anomaly maps at a scale of 1:250,000 are presented for various regional wavelength filters, and a power spectrum of the frequency components in the South Cascade gravity data is displayed. No attempt is made to interpret the results of this study in terms of geologic structures.

  12. Joint Inversion and Forward Modeling of Gravity and Magnetic Data in the Ismenius Region of Mars

    NASA Technical Reports Server (NTRS)

    Milbury, C. A.; Raymond, C. A.; Jewell, J. B.; Smrekar, S. E.; Schubert, G.

    2005-01-01

    The unexpected discovery of remanent crustal magnetism on Mars was one of the most intriguing results from the Mars Global Surveyor mission. The origin of the pattern of magnetization remains elusive. Correlations with gravity and geology have been examined to better understand the nature of the magnetic anomalies. In the area of the Martian dichotomy between 50 and 90 degrees E (here referred to as the Ismenius Area), we find that both the Bouguer and the isostatic gravity anomalies appear to correlate with the magnetic anomalies and a buried fault, and allow for a better constraint on the magnetized crust].

  13. Dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth

    NASA Technical Reports Server (NTRS)

    Revenaugh, Justin; Parsons, Barry

    1987-01-01

    Adopting the formalism of Parsons and Daly (1983), analytical integral equations (Green's function integrals) are derived which relate gravity anomalies and dynamic boundary topography with temperature as a function of wavenumber for a fluid layer whose viscosity varies exponentially with depth. In the earth, such a viscosity profile may be found in the asthenosphere, where the large thermal gradient leads to exponential decrease of viscosity with depth, the effects of a pressure increase being small in comparison. It is shown that, when viscosity varies rapidly, topography kernels for both the surface and bottom boundaries (and hence the gravity kernel) are strongly affected at all wavelengths.

  14. Gravity evidence for a shallow intrusion under Medicine Lake volcano, California.

    USGS Publications Warehouse

    Finn, C.; Williams, D.L.

    1982-01-01

    A positive gravity anomaly is associated with Medicine Lake volcano, California. Trials with different Bouguer reduction densities indicate that this positive anomaly cannot be explained by an inappropriate choice of Bouguer reduction density but must be caused by a subvolcanic body. After separating the Medicine Lake gravity high from the regional field, we were able to fit the 27mgal positive residual anomaly with a large, shallow body of high density contrast (+0.41g/cm3) and a thickness of 2.5km. We interpret this body to be an intrusion of dense material emplaced within the several-kilometres-thick older volcanic layer that probably underlies Medicine Lake volcano.-Authors

  15. Anomalies and Hawking fluxes from the black holes of topologically massive gravity

    NASA Astrophysics Data System (ADS)

    Porfyriadis, Achilleas P.

    2009-05-01

    The anomaly cancelation method proposed by Wilczek et al. is applied to the black holes of topologically massive gravity (TMG) and topologically massive gravito-electrodynamics (TMGE). Thus the Hawking temperature and fluxes of the ACL and ACGL black holes are found. The Hawking temperatures obtained agree with the surface gravity formula. Both black holes are rotating and this gives rise to appropriate terms in the effective U (1) gauge field of the reduced (1 + 1)-dimensional theory. It is found that the terms in this U (1) gauge field correspond exactly to the correct angular velocities on the horizon of both black holes as well as the correct electrostatic potential of the ACGL black hole. So the results for the Hawking fluxes derived here from the anomaly cancelation method, are in complete agreement with the ones obtained from integrating the Planck distribution.

  16. Improved gravity anomaly fields from retracked multimission satellite radar altimetry observations over the Persian Gulf and the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Khaki, M.; Forootan, E.; Sharifi, M. A.; Awange, J.; Kuhn, M.

    2015-09-01

    Satellite radar altimetry observations are used to derive short wavelength gravity anomaly fields over the Persian Gulf and the Caspian Sea, where in situ and ship-borne gravity measurements have limited spatial coverage. In this study the retracking algorithm `Extrema Retracking' (ExtR) was employed to improve sea surface height (SSH) measurements that are highly biased in the study regions due to land contaminations in the footprints of the satellite altimetry observations. ExtR was applied to the waveforms sampled by the five satellite radar altimetry missions: TOPEX/POSEIDON, JASON-1, JASON-2, GFO and ERS-1. Along-track slopes have been estimated from the improved SSH measurements and used in an iterative process to estimate deflections of the vertical, and subsequently, the desired gravity anomalies. The main steps of the gravity anomaly computations involve estimating improved SSH using the ExtR technique, computing deflections of the vertical from interpolated SSHs on a regular grid using a biharmonic spline interpolation and finally estimating gridded gravity anomalies. A remove-compute-restore algorithm, based on the fast Fourier transform, has been applied to convert deflections of the vertical into gravity anomalies. Finally, spline interpolation has been used to estimate regular gravity anomaly grids over the two study regions. Results were evaluated by comparing the estimated altimetry-derived gravity anomalies (with and without implementing the ExtR algorithm) with ship-borne free air gravity anomaly observations, and free air gravity anomalies from the Earth Gravitational Model 2008 (EGM2008). The comparison indicates a range of 3-5 mGal in the residuals, which were computed by taking the differences between the retracked altimetry-derived gravity anomaly and the ship-borne data. The comparison of retracked data with ship-borne data indicates a range in the root-mean-square-error (RMSE) between approximately 1.8 and 4.4 mGal and a bias between 0

  17. Vertical and Horizontal Analysis of Crustal Structure of Southeastern Mediterranean and the Egyptian Coastal Zone, from Bouguer and Satellite Mission Data

    NASA Astrophysics Data System (ADS)

    Saleh, Salah

    2016-07-01

    The present Tectonic system of Southeastern Mediterranean is driven by the collision of the African and Eurasian plates, the Arabian Eurasian convergence and the displacement of the Anatolian Aegean microplate, which generally represents the characteristic of lithospheric structure of the region. In the scope of this study, Bouguer and the satellite gravity (satellite altimetry) anomalies of southeastern Mediterranean and North Eastern part of Egypt were used for investigating the lithospheric structures. Second order trend analyses were applied firstly to Bouguer and satellite altimetry data for examining the characteristic of the anomaly. Later, the vertical and horizontal derivatives applications were applied to the same data. Generally, the purpose of the applying derivative methods is determining the vertical and horizontal borders of the structure. According to the results of derivatives maps, the study area could mainly divided into important four tectonic subzones depending on basement and Moho depth maps. These subzones are distributed from south to the north as: Nile delta-northern Sinai zone, north Egyptian coastal zone, Levantine basin zone and northern thrusting (Cyprus and its surroundings) zone. These zones are separated from each other by horizontal tectonic boundaries and/or near-vertical faults that display the block-faulting tectonic style of this belt. Finally, the gravity studies were evaluated together with the seismic activity of the region. Consequently, the geodynamical structure of the region is examined with the previous studies done in the region. Thus, the current study indicates that satellite gravity mission data is a valuable source of data in understanding the tectonic boundary behavior of the studied region and that satellite gravity data is an important modern source of data in the geodynamical studies.

  18. Mean gravity anomalies and sea surface heights derived from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1978-01-01

    Approximately 2000 GEOS-3 altimeter arcs were analyzed to improve knowledge of the geoid and gravity field. An adjustment procedure was used to fit the sea surface heights (geoid undulations) in an adjustment process that incorporated cross-over constraints. The error model used for the fit was a one or two parameter model which was designed to remove altimeter bias and orbit error. The undulations on the adjusted arcs were used to produce geoid maps in 20 regions. The adjusted data was used to derive 301 5 degree equal area anomalies and 9995 1 x 1 degree anomalies in areas where the altimeter data was most dense, using least squares collocation techniques. Also emphasized was the ability of the altimeter data to imply rapid anomaly changes of up to 240 mgals in adjacent 1 x 1 degree blocks.

  19. Gravity and magnetic anomaly modeling and correlation using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J. (Principal Investigator); Vonfrese, R. R. B.

    1980-01-01

    The spherical Earth inversion, modeling, and contouring software were tested and modified for processing data in the Southern Hemisphere. Preliminary geologic/tectonic maps and selected cross sections for South and Central America and the Caribbean region are being compiled and as well as gravity and magnetic models for the major geological features of the area. A preliminary gravity model of the Andeas Beniff Zone was constructed so that the density columns east and west of the subducted plates are in approximate isostatic equilibrium. The magnetic anomaly for the corresponding magnetic model of the zone is being computed with the SPHERE program. A test tape containing global magnetic measurements was converted to a tape compatible with Purdue's CDC system. NOO data were screened for periods of high diurnal activity and reduced to anomaly form using the IGS-75 model. Magnetic intensity anomaly profiles were plotted on the conterminous U.S. map using the track lines as the anomaly base level. The transcontinental magnetic high seen in POGO and MAGSAT data is also represented in the NOO data.

  20. Spherical Earth analysis and modeling of lithospheric gravity and magnetic anomalies. Ph.D. Thesis - Purdue Univ.

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1980-01-01

    A comprehensive approach to the lithospheric analysis of potential field anomalies in the spherical domain is provided. It has widespread application in the analysis and design of satellite gravity and magnetic surveys for geological investigation.

  1. Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic

    USGS Publications Warehouse

    Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

    2011-01-01

    New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

  2. Principal Facts for Gravity Data Collected in Wisconsin: A Web Site and CD-ROM for Distribution of Data

    USGS Publications Warehouse

    Snyder, Stephen L.; Geister, Daniel W.; Daniels, David L.; Ervin, C. Patrick

    2004-01-01

    Principal facts for 40,488 gravity stations covering the entire state of Wisconsin are presented here in digital form. This is a compilation of previously published data collected between 1948 and 1992 from numerous sources, along with over 10,000 new gravity stations collected by the USGS since 1999. Also included are 550 gravity stations from previously unpublished sources. Observed gravity and complete-Bouguer gravity anomaly data for this statewide compilation are included here. Altogether, 14 individual surveys are presented here.

  3. Probing the Lunar Polar Crust with GRAIL Gravity

    NASA Astrophysics Data System (ADS)

    Smith, D. E.; Zuber, M. T.; Goossens, S. J.; Rowlands, D. D.; Neumann, G. A.; Mazarico, E.; Genova, A.; Lemoine, F. G.

    2015-12-01

    The lunar polar crust, from latitude ±80° to the pole, exhibits Bouguer gravity anomalies that result from crustal density variations of order ±45 mGal in the south and ±25 mGal in the north, bandpass filtered to wavelengths representing the top 50 km. Evident in the Bouguer gravity at both poles are the signatures of a few large craters and basins. But at both poles, the Bouguer map also displays a large number of small, rather sinuous features, some outlining crater rims and some structures on crater floors, that are distributed more or less uniformly across the region. The root mean square (rms) variation over the 10° radius cap is less than 11 mGals at the south pole and less than 7 mGals in the north. This difference reflects the greater crustal complexity in the south compared to the north, but these magnitudes are approximately 10% of the total field in the polar regions, indicating that substantial density anomalies exist below 50 km depth. Modeling the crustal anomalies in the top 50 km by density contrasts at various depths suggest the rms magnitudes can be explained by small local variations in porosity, or possibly the presence of H2O at concentrations of a few percent. The required concentration increases with depth for a given volume but the possibility that the source of the polar anomalies includes small concentrations of H2O in the crust, however, cannot be ruled out.

  4. Joint Interpretation of Bathymetric and Gravity Anomaly Maps Using Cross and Dot-Products.

    NASA Astrophysics Data System (ADS)

    Jilinski, Pavel; Fontes, Sergio Luiz

    2010-05-01

    0.1 Summary We present the results of joint map interpretation technique based on cross and dot-products applied to bathymetric and gravity anomaly gradients maps. According to the theory (Gallardo, Meju, 2004) joint interpretation of different gradient characteristics help to localize and empathize patterns unseen on one image interpretation and gives information about the correlation of different spatial data. Values of angles between gradients and their cross and dot-product were used. This technique helps to map unseen relations between bathymetric and gravity anomaly maps if they are analyzed separately. According to the method applied for the southern segment of Eastern-Brazilian coast bathymetrical and gravity anomaly gradients indicates a strong source-effect relation between them. The details of the method and the obtained results are discussed. 0.2 Introduction We applied this method to investigate the correlation between bathymetric and gravity anomalies at the southern segment of the Eastern-Brazilian coast. Gridded satellite global marine gravity data and bathymetrical data were used. The studied area is located at the Eastern- Brazilian coast between the 20° W and 30° W meridians and 15° S and 25° S parallels. The volcanic events responsible for the uncommon width of the continental shelf at the Abrolhos bank also were responsible for the formation of the Abrolhos islands and seamounts including the major Vitoria-Trindade chain. According to the literature this volcanic structures are expected to have a corresponding gravity anomaly (McKenzie, 1976, Zembruscki, S.G. 1979). The main objective of this study is to develop and test joint image interpretation method to compare spatial data and analyze its relations. 0.3 Theory and Method 0.3.1 Data sources The bathymetrical satellite data were derived bathymetry 2-minute grid of the ETOPO2v2 obtained from NOAA's National Geophysical Data Center (http://www.ngdc.noaa.gov). The satellite marine gravity 1

  5. Calculation of gravity and magnetic anomalies along profiles with end corrections and inverse solutions for density and magnetization

    USGS Publications Warehouse

    Cady, John W.

    1977-01-01

    A computer program is presented which performs, for one or more bodies, along a profile perpendicular to strike, both forward calculations for the magnetic and gravity anomaly fields and independent gravity and magnetic inverse calculations for density and susceptibility or remanent magnetization.

  6. Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel

    2015-03-01

    , the intrusion concentrates bending primarily at the periphery, resulting in a flat, tabular intrusion. We predict that this process will result in concentric fractures over the region of greatest bending. This location is close to the crater wall in large, flat-floored craters, as observed in the crater Humboldt, and interior to the crater over the domed floor in smaller craters, as observed in the crater Vitello. A variety of volcanic features are predicted to be associated with the solidification and degassing of the intrusion; these include: (1) surface lava flows associated with concentric fractures (e.g., in the crater Humboldt); (2) vents with no associated pyroclastic material, from the deflation of under-pressurized magmatic foam (e.g., the crater Damoiseau); and (3) vents with associated pyroclastic deposits from vulcanian eruptions of highly pressurized magmatic foam (e.g., the crater Alphonsus). The intrusion of basaltic magma beneath the crater is predicted to contribute a positive component to the Bouguer gravity anomaly; we assess the predicted Bouguer anomalies associated with FFCs and outline a process for their future interpretation. We conclude that our proposed mechanism serves as a viable formation process for FFCs and accurately predicts numerous morphologic, morphometric, and geophysical features associated with FFCs. These predictions can be further tested using GRAIL (Gravity Recovery and Interior Laboratory) data.

  7. The gravity signature of mantle uplift from impact modeling craters on the Moon

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth S.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2014-11-01

    NASA’s dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution; this has enabled the study of lunar impact craters of all sizes and ages. Soderblom et al. [2014, LPSC abstract #1777] calculated the residual Bouguer anomalies for ~2700 craters 27-184 km in diameter (D). They found that the residual central Bouguer anomaly of craters smaller than 100 km is essentially zero, that there is a transition for 100-150 km, and that craters larger than 184 km have a positive residual Bouguer anomaly that increases with increasing crater size. We use the iSALE shock physics hydrocode to model crater formation, including the effects of porosity and dilatancy (shear bulking). We use strength parameters of gabbroic anorthosite for a 35-km-thick crust, and dunite for the mantle. Our dunite impactors range in size from 6-30 km, which produce craters 86-450 km in diameter. We calculate the Bouguer gravity anomaly due solely to mantle uplift. We eliminate the effects of pressure and temperature on density by setting the output densities from the simulations to 2550 kg/m^3 if they are below the cutoff value of 3000 kg/m^3, and 3220 kg/m^3 if they are above. We compare our modeling results to gravity data from GRAIL. We find that the crater size at which mantle uplift dominates the crater gravity occurs at a crater diameter that is close to the complex crater to peak-ring basin transition. This is in agreement with the observed trend reported by Soderblom et al. [2014, LPSC abstract #1777].

  8. Gravity Survey of the Carson Sink - Data and Maps

    DOE Data Explorer

    Faulds, James E.

    2013-12-31

    A detailed gravity survey was carried out for the entire Carson Sink in western Nevada (Figure 1) through a subcontract to Zonge Engineering, Inc. The Carson Sink is a large composite basin containing three known, blind high‐temperature geothermal systems (Fallon Airbase, Stillwater, and Soda Lake). This area was chosen for a detailed gravity survey in order to characterize the gravity signature of the known geothermal systems and to identify other potential blind systems based on the structural setting indicated by the gravity data. Data: Data were acquired at approximately 400, 800, and 1600 meter intervals for a total of 1,243 stations. The project location and station location points are presented in Figure 14. The station distribution for this survey was designed to complete regional gravity coverage in the Carson Sink area without duplication of available public and private gravity coverage. Gravity data were acquired using a Scintrex CG‐5 gravimeter and a LaCoste and Romberg (L&R) Model‐G gravimeter. The CG‐5 gravity meter has a reading resolution of 0.001 milligals and a typical repeatability of less than 0.005 milligals. The L&R gravity meter has a reading resolution of 0.01 milligals and a typical repeatability of 0.02 milligals. The basic processing of gravimeter readings to calculate through to the Complete Bouguer Anomaly was made using the Gravity and Terrain Correction software version 7.1 for Oasis Montaj by Geosoft LTD. Results: The gravity survey of the Carson Sink yielded the following products. Project location and station location map (Figure 14). Complete Bouguer Anomaly @ 2.67 gm/cc reduction density. Gravity Complete Bouguer Anomaly at 2.50 g/cc Contour Map (Figure 15). Gravity Horizontal Gradient Magnitude Shaded Color Contour Map. Gravity 1st Vertical Derivative Color Contour Map. Interpreted Depth to Mesozoic Basement (Figure 16), incorporating drill‐hole intercept values. Preliminary Interpretation of Results: The Carson Sink

  9. Subsurface structure of Teboursouk and El Krib plains (dome zone, northern Tunisia) by gravity analysis

    NASA Astrophysics Data System (ADS)

    Hadhemi, Balti; Fatma, Hachani; Ali, Kadri; Mohamed, Gasmi

    2016-07-01

    Gravity data was used to investigate sub-surface structure of the Teboursouk and El Krib plains belonging to the dome zone in the Northwest of Tunisia. Analysis of the gravity data included the computation of the Bouguer anomaly, the horizontal and vertical gravity gradients, the upward continuations, Euler deconvolution and analytic signal of high-resolution. The Bouguer anomaly map (d = 2.4 g cm-3) has provided information on the variation of the underground density and shown contrasting anomalous zones. The treatments applied to the Bouguer anomaly map have detected new deep faults and provided details on their dips and depths (exceeding 1500 m per places). Statistical analysis of the gravity data filtering shows that the study area is divided by four major faults with NW-SE, NE-SW, E-W and N-S trends. These faults have contributed to the structuring of the area. The results provide confirmation of some faults already recognized or inferred from the previous structural studies, and specify their depths and dips. While large number of new faults that remained undetected until now, have been highlighted.

  10. Crustal structure beneath the southern Appalachians: nonuniqueness of gravity modeling

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Grow, John A.; Klitgord, Kim D.

    1983-01-01

    Gravity models computed for a profile across the long-wavelength paired negative-positive Bouguer anomalies of the southern Appalachian Mountains show that the large negative anomaly can be explained by a crustal root zone, whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries: a suture zone, a mantle upwarp, or a shallow body. Seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly. The presence of outcropping mafic and ultramafic rocks in the southern Appalachians and the inferred tectonic history of the Appalachian orogen are most consistent with the suture-zone model. Crust similar to continental crust probably exists beneath the Coastal Plain and inner continental shelf where the gravity anomalies return to near-zero values.

  11. A harmonic analysis of lunar gravity

    NASA Technical Reports Server (NTRS)

    Bills, B. G.; Ferrari, A. J.

    1980-01-01

    An improved model of lunar global gravity has been obtained by fitting a sixteenth-degree harmonic series to a combination of Doppler tracking data from Apollo missions 8, 12, 15, and 16, and Lunar Orbiters 1, 2, 3, 4, and 5, and laser ranging data to the lunar surface. To compensate for the irregular selenographic distribution of these data, the solution algorithm has also incorporated a semi-empirical a priori covariance function. Maps of the free-air gravity disturbance and its formal error are presented, as are free-air anomaly and Bouguer anomaly maps. The lunar gravitational variance spectrum has the form V(G; n) = O(n to the -4th power), as do the corresponding terrestrial and martian spectra. The variance spectra of the Bouguer corrections (topography converted to equivalent gravity) for these bodies have the same basic form as the observed gravity; and, in fact, the spectral ratios are nearly constant throughout the observed spectral range for each body. Despite this spectral compatibility, the correlation between gravity and topography is generally quite poor on a global scale.

  12. Sedimentary basin analysis using airborne gravity data: a case study from the Bohai Bay Basin, China

    NASA Astrophysics Data System (ADS)

    Li, Wenyong; Liu, Yanxu; Zhou, Jianxin; Zhou, Xihua; Li, Bing

    2015-12-01

    In this paper, we discuss the application of an airborne gravity survey to sedimentary basin analysis. Using high-precision airborne gravity data constrained by drilling and seismic data from the Bohai Bay Basin in eastern China, we interpreted faults, structural elements, sedimentary thickness, structural styles and local structures (belts) in the central area of the Basin by the wavelet transform method. Subsequently, these data were subtracted from the Bouguer gravity to calculate the residual gravity anomalies. On this basis, the faults were interpreted mainly by linear zones of high gravity gradients and contour distortion, while the sedimentary thicknesses were computed by the Euler deconvolution. The structural styles were identified by the combination of gravity anomalies and the local structures interpreted by the first vertical derivative of the residual gravity. The results showed evidence for seven faults, one sag and ten new local structure belts.

  13. Pre-impact crustal porosity and its effect on the gravity signature of lunar craters

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth C.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2015-04-01

    NASA's dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution. Soderblom et al. [2015] made a comprehensive analysis of the residual and central uplift Bouguer gravity anomalies associated with more than 5200 lunar craters. There were two main observations that are related to the work presented here: 1) craters less than ~150 km in diameter (D) have a residual Bouguer anomaly (BA) that is near zero on average (although a negative trend is observed), but have both positive and negative anomalies that vary by approximately ±25 mGal about the mean, and, 2) there is a transition at which the central uplift BA becomes positive and increases with D. Craters that are located in the maria and South Pole-Aitken (SPA) basin were excluded from the analysis because they tend to have more negative signatures than highlands craters. These gravitational signatures contrast with the invariably negative gravity anomalies associated with terrestrial craters. In this study, we investigate pre-impact porosity by modeling crater formation using the iSALE hydrocode, including a new approach to include dilatancy, to determine their effects on the gravity signature of craters. We calculated the BA for the simulations, but due to mantle uplift alone. We find that the magnitude of the BA increases with increasing porosity, and that variable initial porosity of the lunar crust can explain why craters on the Moon exhibit both positive and negative Bouguer anomalies. This can also explain the observed negative residual BA associated with craters formed in the lunar maria and SPA (and associated melt sheet) because they are typically less porous than the highlands crust. Gravity anomalies due to mantle uplift reproduce the observed transition from zero to a positive central uplift BA, which coincides with the morphological transition from complex craters to peak-ring basins.

  14. Gravity anomalies and the structure of western Tibet and the southern Tarim Basin

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, H.; Molnar, P.

    1984-01-01

    Gravity anomalies across the western part of the Tarim Basin and the Kunlun mountain belt show that this area is not in local isostatic equilibrium. These data can be explained if a strong plate underlying the Tarim Basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest Tibet. This corroborates Norin's inference that late Tertiary crustal shortening has occurred in this area by southward underthrusting of the Tarim Basin beneath the Kunlun. This study places a lower bound on the amount of underthrusting.

  15. Interpretation of Gravity Anomalies with the Normalized Full Gradient (NFG) Method and an Example

    NASA Astrophysics Data System (ADS)

    Aydin, Ali

    2007-12-01

    The Normalized Full Gradient (NFG) method which was put forward about 50 years ago has been used for downward continuation of gravity potential data, especially in the former Union of Soviet Socialist Republics. This method nullifies perturbations due to the passage of mass depth during downward continuation. The method depends on the downwards analytical continuation of normalized full gradient values of gravity data. Analytical continuation discriminates certain structural anomalies which cannot be distinguished in the observed gravity field. This method has been used in various petroleum and tectonic studies. The Trapeze method was used for the determination of Fourier coefficients during the application of this method. No other techniques for calculating these coefficients have been used. However, the Filon method was used for the determination of Fourier coefficients during the application of the NFG method in this work. This method, rather than the Trapeze method, should be preferred for indicating abnormal mass resources at the lower harmonics. In this study, the NFG method using the Filon method has been applied the first time to theoretical models of gravity profiles as example field at the Hasankale-Horasan petroleum exploration province where successful results were achieved. Hydrocarbon presence was shown on the NFG sections by the application of NFG downward continuation operations on theoretical models. Important signs of hydrocarbon structure on the NFG section for field and model data at low harmonics are obtained more effectively using this method.

  16. Modeling of shallow structures in the Cappadocia region using gravity and aeromagnetic anomalies

    NASA Astrophysics Data System (ADS)

    Kosaroglu, Sinan; Buyuksarac, Aydin; Aydemir, Attila

    2016-07-01

    In this study, shallow structures and bodies creating gravity and magnetic anomalies in the Cappadocia Volcanic Complex region in central Anatolia were investigated in order to determine the tectonic origin and structural setting of young volcanic units. The shallow geological structures in the region are depressions filled with mainly low-density, loose volcano-clastics and ignimbrite sheets associated with the continental Neogene deposits. These units together with other volcanic products are originated from the large Neogene and Quaternary volcanoes of the central Anatolia, particularly in the Cappadocia region. At first, spectral analysis to obtain the cut-off frequencies for the high-pass filter was performed in this investigation. Then, gravity and magnetic data were high-pass filtered to remove the deep and regional effects on anomalies and to unveil only shallow structures' effects. Subsequently, upward and downward continuations were carried out to determine how these shallow structures influence the total anomalies and their contribution in the confining total potential field. In addition, three and two dimensional gravity models (3D and 2D) of the study area were also constructed to obtain the bottom depth of shallow bodies. According to spectral analysis results, shallow structures could be separated into two groups from the power spectrums and bottom depth of deeper structure was commonly determined about 2 km in gravity and magnetic spectrum, both. More shallow structure is at the depth around 0.317 km according to the gravity power spectrum. Obviously, 3D and 2D models are consistent with the spectral analysis results for the deeper unit depth. A circular, large depression (70 × 50 km2) surrounds Mount Melendiz with a 1-2.7 km depth range (2 km in average). Because the depressions around the central volcanoes of Mount Melendiz and Mount Hasan cover very large areas in the basin scale, the shallow and low-density volcanic units can hardly be claimed

  17. Genesis of the largest Amazonian wetland in northern Brazil inferred by morphology and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Rossetti, Dilce de Fátima; Cassola Molina, Eder; Cremon, Édipo Henrique

    2016-08-01

    The Pantanal Setentrional (PS) is the second largest wetland in Brazil, occurring in a region of northern Amazonia previously regarded as part of the intracratonic Solimões Basin. However, while Paleozoic to Neogene strata are recorded in this basin, the PS constitutes a broad region with an expressive record of only Late Pleistocene and Holocene deposits. The hypothesis investigated in the present work is if these younger deposits were formed within a sedimentary basin having a geological history separated from the Solimões Basin. Due to the location in a remote region of low accessibility, the sedimentary fill of the PS wetland remains largely unknown in subsurface. In the present work, we combine geomorphological and gravity data acquired on a global basis by several satellite gravity missions to approach the geological context of this region. The results revealed a wetland characterized in surface by a low-lying terrain with wedge shape and concave-up geometry that is in sharp contact with highland areas of Precambrian rocks of the Guiana Shield. Such contact is defined by a series of mainly NE- or NW-trending straight lineaments that eventually extend into both the Guiana Shield and the PS wetland. Also of relevance is that a great part of the PS wetland sedimentary cover consists of dominantly sandy deposits preserved as residual paleo-landforms with triangular shapes previously related to megafan depositional systems. These are distributed radially at the northern margin of the PS, with axis toward basement rocks and fringes toward the wetland's center, the latter containing the largest megafan landform. The analysis of gravity anomaly data revealed a main NNE-trending chain ∼500 km in length defined by high gravity values (i.e., up to 60 mGal); these are bounded by negative anomalies as low as -90 mGal. The chain with positive gravity anomaly marks the center of a subsiding area having a geological evolution that differs from the adjacent intracratonic

  18. Anomalies.

    ERIC Educational Resources Information Center

    Online-Offline, 1999

    1999-01-01

    This theme issue on anomalies includes Web sites, CD-ROMs and software, videos, books, and additional resources for elementary and junior high school students. Pertinent activities are suggested, and sidebars discuss UFOs, animal anomalies, and anomalies from nature; and resources covering unexplained phenonmenas like crop circles, Easter Island,…

  19. Principal facts for gravity stations in the Elko, Steptoe Valley, Coyote Spring Valley, and Sheep Range areas, eastern and southern Nevada

    USGS Publications Warehouse

    Berger, D.L.; Schaefer, D.H.; Frick, E.A.

    1990-01-01

    Principal facts for 537 gravity stations in the carbonate-rock province of eastern and southern Nevada are tabulated and presented. The gravity data were collected in support of groundwater studies in several valleys. The study areas include the Elko area, northern Steptoe Valley, Coyote Spring Valley, and the western Sheep Range area. The data for each site include values for latitude, longitude, altitude, observed gravity, free- air anomaly, terrain correction, and Bouguer anomaly (calculated at a bedrock density of 2.67 g/cu cm. (USGS)

  20. Gravity Anomaly Between Immature And Mature Subduction Zones In The Western Pacific And Its Implications For Subduction Evolution

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Lee, S.

    2008-12-01

    From immature to mature subduction zones, the western Pacific is a key area to investigate subduction evolution. Among them, the Yap and Mussau trenches located in the boundary of Caroline plate and the Hjort trench to the south of New Zealand are considered as immature subduction zones. The common geological features of immature subduction zones include: (1) a short trench-arc distance, (2) the lack of Wadati-Benioff zone, and (3) the absence of arc volcanism triggered by subducting slab. On the other hand, the Izu-Bonin- Mariana and Tonga-Kermadec trenches are well-developed or mature subduction zones characterized by active arc volcanism and deep earthquakes. We compare two end-members, immature and mature subduction zones, with gravity anomaly derived from satellite altimetry which has sufficient accuracy for this kind of regional study. The isostatic residual gravity anomalies show that the width of non-isostatically- compensated region of the mature subduction zone is substantially wider than that of immature ones. Moreover, when we removed the gravitational effects due to the seafloor from the free-air gravity anomaly, a large difference was found between the immature and mature subduction zones in the overriding plate side. In the mature subduction zones, a low gravity anomaly of ~200-250 mGals can be found in the overriding plate which differs from the immature subduction zones. We discuss the possible causes of the low gravity anomaly including: (1) serpentinization in the upper mantle; (2) presence of partial melt in the mantle wedge; (3) difference in the density structure between the overriding and subducting plates in terms of slab age and cooling history; and (4) thickened crust or anomalous crustal structure beneath the arc. Serpentinization cannot explain the low gravity anomaly at ~150-200 km from the trench. Also, the difference of gravity anomaly due to the difference of the slab age is insufficient to account for the total anomaly. In this

  1. Interpretation of gravity and magnetic anomalies at Lake Rotomahana: Geological and hydrothermal implications

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, F.; de Ronde, C. E. J.; Scott, B. J.; Soengkono, S.; Stagpoole, V.; Timm, C.; Tivey, M.

    2016-03-01

    We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest that subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalt dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.

  2. 3D free-air gravity anomaly modeling for the Southeast Indian Ridge

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Heyde, Ingo; Rinaldo Barchi, Massimiliano; Pauselli, Cristina

    2016-04-01

    In this study we analyzed the free-air gravity anomalies measured on the northwestern part of the Southeast Indian Ridge (hereafter SEIR) during the BGR cruise INDEX2012 with RV FUGRO GAUSS. The survey area covered the ridge from the Rodriguez Triple Junction along about 500 km towards the SSE direction. Gravity and magnetic data were measured along 65 profiles with a mean length of 60 km running approximately perpendicular to the ridge axis. The final gravity data were evaluated every 20 seconds along each profile. This results in a sampling interval of about 100 m. The mean spacing of the profiles is about 7 km. Together with the geophysical data also the bathymetry was measured along all profiles with a Kongsberg Simrad EM122 multibeam echosounder system. Previous studies reveal that the part of the ridge covered by the high resolution profiles is characterized by young geologic events (the oldest one dates back to 1 Ma) and that the SEIR is an intermediate spreading ridge. We extended the length of each profile to the area outside the ridge, integrating INDEX2012 high resolution gravity and bathymetric data with low resolution data derived from satellite radar altimeter measurements. The 3D forward gravity modeling made it possible to reconstruct a rough crustal density model for an extended area (about 250000 km2) of the SEIR. We analyzed the gravity signal along those 2D sections which cross particular geological features (uplifted areas, accommodation zones, hydrothermal fields and areas with hints for extensional processes e.g. OCCs) in order to establish a correlation between the gravity anomaly signal and the surface geology. We started with a simple "layer-cake" geologic model consisting of four density bodies which represent the sea, upper oceanic crust, lower oceanic crust and the upper mantle. Considering that in the study area the oceanic crust is young, we did not include the sediment layer. We assumed the density values of these bodies considering

  3. Interpretation of subsurface structure using gravity data from region of Appalachian ultradeep hole

    SciTech Connect

    Williams, R.T.; Favret, P.; Fabbri, L.; Chavez-Perez, S.

    1986-05-01

    More than 5000 new gravity measurements have been made over an area of 7500 km/sup 2/ in the region of the proposed ultradeep core hole in the southern Appalachians (ADCOH). Data were obtained mostly at surveyed elevations at approximately 0.5-km intervals along highways, and county and US Forest Service roads in the study area. The data have been reduced to simple Bouguer anomaly values using a standard crustal density of 2.67 g/cc and the International Gravity Formula of 1967. Simple Bouguer anomaly values range from about -10 to -80 mgal within the study area. Profiles crossing the outcrop of the Brevard fault zone (BFZ) at different locations reveal a characteristic gravity signature, with a decrease in gravity of more than 1.5 mgal. A profile along the route of ADCOH seismic line 3, located along US Highway 64 west of Hayesville, North Carolina, crosses a gravity high with an amplitude of more than 50 mgal. A contour map of simple Bouguer anomaly values reveals a linear gravity high of about 4 mgal, trending about N10/sup 0/E, that crosses ADCOH seismic line 1 northwest of Westminster, South Carolina, and seismic line 3 at its intersection with the BFZ. This anomaly correlates with a family of basement faults having more than 0.5 km of throw, seen on both seismic lines 1 and 3, and is evidence that these faults are oblique to both the trend of surface structure and the direction of the seismic profiles. Low gravity values are observed near the Shooting Creek window and Tallulah Falls dome, indicating that these structures may be cored by low-density, possibly sedimentary rocks.

  4. Relation of MAGSAT and Gravity Anomalies to the Main Tectonic Provinces of South America. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Yuan, D. W.

    1984-01-01

    Magnetic anomalies of the South American continent are generally more positive and variable than the oceanic anomalies. There is better correlation between the magnetic anomalies and the major tectonic elements of the continents than between the anomalies and the main tectonic elements of the adjacent oceanic areas. Oceanic areas generally show no direct correlation to the magnetic anomalies. Precambrian continental shields are mainly more magnetic than continental basins and orogenic belts. Shields differ markedly from major aulacogens which are generally characterized by negative magnetic anomalies and positive gravity anomalies. The Andean orogenic belt shows rather poor correlation with the magnetic anomalies. The magnetic data exhibit instead prominent east-west trends, which although consistent with some tectonic features, may be related to processing noise derived from data reduction procedures to correct for external magnetic field effects. The pattern over the Andes is sufficiently distinct from the generally north trending magnetic anomalies occurring in the adjacent Pacific Ocean to separate effectively the leading edge of the South American Plate from the Nazea Plate. Eastern South America is characterized by magnetic anomalies which commonly extend across the continental margin into the Atlantic Ocean.

  5. Preimpact porosity controls the gravity signature of lunar craters

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, H. J.; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Nimmo, F.; Bierson, C. J.; Phillips, R. J.; Zuber, M. T.

    2015-11-01

    We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result from pore space creation due to fracturing and dilatant bulking, and positive anomalies result from destruction of pore space due to shock wave compression. The central BA of craters larger than ~215 km in diameter, however, are invariably positive because of an underlying central mantle uplift. We conclude that the striking differences between the gravity signatures of craters on the Earth and Moon are the result of the higher average porosity and variable porosity of the lunar crust.

  6. Gravity anomalies, flexure and mantle rheology seaward of Circum-Pacific trenches

    NASA Astrophysics Data System (ADS)

    Hunter, J.; Watts, A. B.

    2016-07-01

    We have used ensemble averages of satellite-derived free-air gravity anomaly data, together with inverse modelling techniques, to determine the effective elastic thickness, Te, of circum-Pacific subducting oceanic lithosphere and its relationship to plate age. Synthetic modelling tests show that Te can be recovered best using gravity anomaly, rather than bathymetry, data and profiles that are at least 750 km long. Inverse modeling based on a uniform Te elastic plate suggests that Te increases with age of the subducting oceanic lithosphere and is given approximately by the depth to the 390 ± 10°C oceanic isotherm based on a cooling plate model. Misfits between the observed and calculated gravity anomalies are significantly improved if a mechanically weak zone is included between the trench axis and the outer rise. This weak zone is coincident with observations of bend-faulting and seismicity. Inverse modelling shows that Te landward of the outer rise is generally 40-65% less than the Te seaward of the outer rise. Both landward and seaward Te increases with age of the lithosphere and are given by the depth to the 342-349°C and 671-714°C oceanic isotherm respectively. A dependence of Te on age is consistent with models for the cooling of oceanic lithosphere as it moves away from a mid-ocean ridge and the temperature-dependent ductile creep of oceanic lithospheric minerals such as olivine. By comparing the observed Te to the predicted Te based on laboratory-derived yield strength envelopes and an assumption of elastic-perfectly plastic deformation, we have attempted to constrain the rheology of oceanic lithosphere. Regardless of the assumed friction coefficient, the dry-olivine low-temperature plasticity flow laws of Goetze (1978), Evans & Goetze (1979), Raterron et al. (2004) and Mei et al. (2010) all provide quite a good fit to the observed Te at circum-Pacific subduction zones. This result contrasts with the Hawaiian Islands, where these flow laws are generally

  7. The effect of spatial truncation error on variance of gravity anomalies derived from inversion of satellite orbital and gradiometric data

    NASA Astrophysics Data System (ADS)

    Eshagh, Mehdi; Ghorbannia, Morteza

    2014-07-01

    The spatial truncation error (STE) is a significant systematic error in the integral inversion of satellite gradiometric and orbital data to gravity anomalies at sea level. In order to reduce the effect of STE, a larger area than the desired one is considered in the inversion process, but the anomalies located in its central part are selected as the final results. The STE influences the variance of the results as well because the residual vector, which is contaminated with STE, is used for its estimation. The situation is even more complicated in variance component estimation because of its iterative nature. In this paper, we present a strategy to reduce the effect of STE on the a posteriori variance factor and the variance components for inversion of satellite orbital and gradiometric data to gravity anomalies at sea level. The idea is to define two windowing matrices for reducing this error from the estimated residuals and anomalies. Our simulation studies over Fennoscandia show that the differences between the 0.5°×0.5° gravity anomalies obtained from orbital data and an existing gravity model have standard deviation (STD) and root mean squared error (RMSE) of 10.9 and 12.1 mGal, respectively, and those obtained from gradiometric data have 7.9 and 10.1 in the same units. In the case that they are combined using windowed variance components the STD and RMSE become 6.1 and 8.4 mGal. Also, the mean value of the estimated RMSE after using the windowed variances is in agreement with the RMSE of the differences between the estimated anomalies and those obtained from the gravity model.

  8. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Ali A. Nowroozi; John Leftwich

    1997-12-31

    Our research to date has involved the Interpretation of the Bouguer Gravity Anomaly Associated with the Richmond and Taylorsville Triassic Basins and its Vicinity. Continental rift basins around the world contain about 5% of the earth's sedimentary layers and produce about 20% of the total hydrocarbon production of the world (Ziegler (1983). Nearly 30 large basins of this type are reported by Manspeizer and Cousminer (1988) in eastern North America and northwestern Africa. There are eleven exposed basins of this type in the state of Virginia, from which nine are totally and two partially within the state's border. The number of unexposed basin's is not known. Exploration and drilling have been hampered largely because surface data are insufficient for even evaluation of those basins which are partly or completely exposed in the Piedmont Province. Generation of data through random exploratory drilling and seismic exploration is much too expensive and, therefore, these methods have not been widely used. In order to remedy this situation, we have used a geophysical method and completed a detailed and dense ground gravity surveys of the Richmond (Nowroozi and Wong, 1989, Daniels and Nowroozi, 1987). In this work we report our progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this progress report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  9. Spectral analysis of GEOS-3 altimeter data and frequency domain collocation. [to estimate gravity anomalies

    NASA Technical Reports Server (NTRS)

    Eren, K.

    1980-01-01

    The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.

  10. Implications of the Utopia Gravity Anomaly for the Resurfacing of the Northern Plains of Mars

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.

    2004-01-01

    Whereas the surface units of the northern plain of Mars generally exhibit ages ranging from late Hesperian to Amazonian, interpretation of precise topographic measurements indicate that the age of the underlying "basement" is early Noachian, or almost as old as the southern highlands. This suggests that widespread but relatively superficial resurfacing has occurred throughout the northern plains since the end of early heavy bombardment. In this abstract I examine some of the possible implications of the subsurface structure inferred for the Utopia basin from gravity data on the nature of this resurfacing. The large, shallow, circular depression in Utopia Planitia has been identified as a huge impact basin, based on both geological evidence and detailed analysis of MOLA topography. Its diameter (approx. 3000 km) is equivalent to that of the Hellas basin, as is its inferred age (early Noachian). However, whereas Hellas is extremely deep with rough terrain and large slopes, the Utopia basin is a smooth, shallow, almost imperceptible bowl. Conversely, Utopia displays one of the largest (non-Tharsis-related) positive geoid anomalies on Mars, in contrast to a much more subdued negative anomaly over Hellas.

  11. Fluid/Gravity Correspondence, Second Order Transport and Gravitational Anomaly***

    NASA Astrophysics Data System (ADS)

    Megías, Eugenio; Pena-Benitez, Francisco

    2014-03-01

    We study the transport properties of a relativistic fluid affected by chiral and gauge-gravitational anomalies. The computation is performed in the framework of the fluid/gravity correspondence for a 5 dim holographic model with Chern-Simons terms in the action. We find new anomalous and non anomalous transport coefficients, as well as new contributions to the existing ones coming from the mixed gauge-gravitational anomaly. Consequences for the shear waves dispersion relation are analyzed. Talk given by E. Megías at the International Nuclear Physics Conference INPC 2013, 2-7 June 2013, Firenze, Italy.Supported by Plan Nacional de Altas Energías (FPA2009-07908, FPA2011-25948), Spanish MICINN Consolider-Ingenio 2010 Programme CPAN (CSD2007-00042), Comunidad de Madrid HEP-HACOS S2009/ESP-1473, Spanish MINECO's Centro de Excelencia Severo Ochoa Program (SEV-2012-0234, SEV-2012-0249), and the Juan de la Cierva Program.

  12. Isostatic gravity map of the Monterey 30 x 60 minute quadrangle and adjacent areas, California

    USGS Publications Warehouse

    Langenheim, V.E.; Stiles, S.R.; Jachens, R.C.

    2002-01-01

    The digital dataset consists of one file (monterey_100k.iso) containing 2,385 gravity stations. The file, monterey_100k.iso, contains the principal facts of the gravity stations, with one point coded per line. The format of the data is described below. Each gravity station has a station name, location (latitude and longitude, NAD27 projection), elevation, and an observed gravity reading. The data are on the IGSN71 datum and the reference ellipsoid is the Geodetic Reference System 1967 (GRS67). The free-air gravity anomalies were calculated using standard formulas (Telford and others, 1976). The Bouguer, curvature, and terrain corrections were applied to the free-air anomaly at each station to determine the complete Bouguer gravity anomalies at a reduction density of 2.67 g/cc. An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography.

  13. An integrated airborne gravity survey of an offshore area near the northern Noto Peninsula, Japan

    NASA Astrophysics Data System (ADS)

    Komazawa, Masao; Okuma, Shigeo; Segawa, Jiro

    2010-02-01

    An airborne gravity survey using a helicopter was carried out in October 2008, offshore along the northern Noto Peninsula, to understand the shallow and regional underground structure. Eleven flight lines, including three tie lines, were arranged at 2km spacing within 20km of the coast. The total length of the flight lines was ~700km. The Bouguer anomalies computed from the airborne gravimetry are consistent with those computed from land and shipborne gravimetry, which gradually decrease in the offshore direction. So, the accuracy of the airborne system is considered to be adequate. A local gravity low in Wajima Bay, which was already known from seafloor gravimetry, was also observed. This suggests that the airborne system has a structural resolution of ~2km. Reduction of gravity data to a common datum was conducted by compiling the three kinds of gravity data, from airborne, shipborne, and land surveys. In the present study, we have used a solid angle numerical integration method and an iteration method. We finally calculated the gravity anomalies at 300m above sea level. We needed to add corrections of 2-5mGals in order to compile the airborne and shipborne gravity data smoothly, so the accuracy of the Bouguer anomaly map is considered to be nearly 2mGal on the whole, and 5mGals at worst in limited or local areas.

  14. The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1982-01-01

    Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

  15. Modelling the gravity and magnetic field anomalies of the Chicxulub crater

    NASA Technical Reports Server (NTRS)

    Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

    1993-01-01

    The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

  16. Detection of Characteristic Precipitation Anomaly Patterns of El Nino / La Nina in Time- variable Gravity Fields by GRACE

    NASA Astrophysics Data System (ADS)

    Heki, K.; Morishita, Y.

    2007-12-01

    GRACE (Gravity Recovery and Climate Experiment) satellites, launched in March 2002, have been mapping monthly gravity fields of the Earth, allowing us to infer changes in surface mass, e.g. water and ice. Past findings include the ice mass loss in southern Greenland (Luthcke et al., 2006) and its acceleration in 2004 (Velicogna and Wahr, 2006), crustal dilatation by the 2004 Sumatra Earthquake (Han et al., 2006) and the postseismic movement of water in mantle (Ogawa and Heki, 2007). ENSO (El Nino and Southern Oscillation) brings about global climate impacts, together with its opposite phenomenon, La Nina. Ropelewski and Halpert (1987) showed typical precipitation patterns in ENSO years; characteristic regional-scale precipitation anomalies occur in India, tropical and southern Africa and South America. Nearly opposite precipitation anomalies are shown to occur in La Nina years (Ropelewski and Halpert, 1988). Here we report the detection of such precipitation anomaly patterns in the GRACE monthly gravity data 2002 - 2007, which includes both La Nina (2005 fall - 2006 spring) and El Nino (2006 fall - 2007 spring) periods. We modeled the worldwide gravity time series with constant trends and seasonal changes, and extracted deviations of gravity values at two time epochs, i.e. February 2006 and 2007, and converted them into the changes in equivalent surface water mass. East Africa showed negative gravity deviation (-20.5 cm in water) in 2006 February (La Nina), which reversed to positive (18.7 cm) in 2007 February (El Nino). Northern and southern parts of South America also showed similar see-saw patterns. Such patterns closely resemble to those found meteorologically (Ropelewski and Halpert, 1987; 1988), suggesting the potential of GRACE as a sensor of inter-annual precipitation anomalies through changes in continental water storage. We performed numerical simulations of soil moisture changes at grid points in land area incorporating the CMAP precipitation data, NCEP

  17. Principal facts for gravity stations in the Nevada portion of the Kingman 1 degree by 2 degree quadrangle

    NASA Astrophysics Data System (ADS)

    Bracken, R. E.; Kane, M. F.

    The principal facts contained in the tables of this report document 862 gravity stations in the Nevada portion of the Kingman 1 degree x 2 degree quadrangle. Two data sets are documented: 193 stations by the USGS, and 669 from the Department of Defense gravity data file. The description of the USGS stations includes gravity meter used, base station locations and values, elevation sources and errors, data reduction methods, and Bouguer anomaly error analysis. Only principal facts are listed for the Department of Defense data. All stations have been terrain corrected.

  18. The gravity anomaly field in the Gulf of Bothnia spatially characterized from satellite altimetry and in situ measurements

    NASA Astrophysics Data System (ADS)

    Noréus, J. P.; Nyborg, M. R.; Hayling, K. L.

    1997-06-01

    The gravity anomaly field in the Gulf of Bothnia has been investigated using (1) in situ high-precision measurements conducted on the sea ice during cold winters, and (2) gravity anomaly profiles computed from collinear satellite radar altimeter data from the Geosat ERM and the Topex/Poseidon missions. The in situ measurements were obtained from a collaboration between the Finnish Geodetic Institute, the Geological Survey of Sweden (SGU) and the National Survey of Sweden (LMV), and were processed with the geostatistical method called kriging. These data were used to calibrate the altimetric gravity. Altimetry generally resolves features of 20 km wavelength or longer, and in some cases detects shorter features when a sampling interval of 10 Hz is used. The precision of the along-track one-dimensional altimetric profiles corresponds to a gravity uncertainty of 2-3 mGal, and comparison with in situ measured gravity show 4 mGal discrepancy. The precision of the in situ measurements is better. However, depending on the sampling distance, the estimation uncertainty interior the in situ data areas may be up to 5 mGal between neighbouring data points. In regions with in situ data gaps, the estimation uncertainty of the in situ gravity measurements is rapidly increasing to a maximum of 9 mGal. An improved estimation uncertainty of 4-9 mGal was obtained in the same data gap regions with the support of satellite altimetry. Altimetric gravity is therefore used to estimate the gravity field in such regions, and to spatially characterize the gravity field in the Gulf of Bothnia.

  19. Estimation of regional mass anomalies from Gravity Recovery and Climate Experiment (GRACE) over Himalayan region

    NASA Astrophysics Data System (ADS)

    Agrawal, R.; Singh, S. K.; Rajawat, A. S.; Ajai

    2014-11-01

    Time-variable gravity changes are caused by a combination of postglacial rebound, redistribution of water and snow/ice on land and as well as in the ocean. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, launched in 2002, provides monthly average of the spherical harmonic co-efficient. These spherical harmonic co-efficient describe earth's gravity field with a resolution of few hundred kilometers. Time-variability of gravity field represents the change in mass over regional level with accuracies in cm in terms of Water Equivalent Height (WEH). The WEH reflects the changes in the integrated vertically store water including snow cover, surface water, ground water and soil moisture at regional scale. GRACE data are also sensitive towards interior strain variation, surface uplift and surface subsidence cover over a large area. GRACE data was extracted over the three major Indian River basins, Indus, Ganga and Brahmaputra, in the Himalayas which are perennial source of fresh water throughout the year in Northern Indian Plain. Time series analysis of the GRACE data was carried out from 2003-2012 over the study area. Trends and amplitudes of the regional mass anomalies in the region were estimated using level 3 GRACE data product with a spatial resolution at 10 by 10 grid provided by Center for Space Research (CSR), University of Texas at Austin. Indus basin has shown a subtle decreasing trend from 2003-2012 however it was observed to be statistically insignificant at 95 % confidence level. Ganga and Brahmaputra basins have shown a clear decreasing trend in WEH which was also observed to be statistically significant. The trend analysis over Ganga and Brahamputra basins have shown an average annual change of -1.28 cm and -1.06 cm in terms of WEH whereas Indus basin has shown a slight annual change of -0.07 cm. This analysis will be helpful to understand the loss of mass in terms of WEH over Indian Himalayas and will be crucial for hydrological and

  20. A gravity model for the Coso geothermal area, California

    SciTech Connect

    Feighner, M.A.; Goldstein, N.E.

    1990-08-01

    Two- and three-dimensional gravity modeling was done using gridded Bouguer gravity data covering a 45 {times} 45 km region over the Coso geothermal area in an effort to identify features related to the heat source and to seek possible evidence for an underlying magma chamber. Isostatic and terrain corrected Bouguer gravity data for about 1300 gravity stations were obtained from the US Geological Survey. After the data were checked, the gravity values were gridded at 1 km centers for the area of interest centered on the Coso volcanic field. Most of the gravity variations can be explained by two lithologic units: (1) low density wedges of Quarternary alluvium with interbedded thin basalts (2.4 g/cm{sup 3}) filling the Rose Valley and Coso Basin/Indian Wells Valley, and (2) low density cover of Tertiary volcanic rocks and intercalated Coso Formation (2.49 g/cm{sup 3}). A 3-D iterative approach was used to find the thicknesses of both units. The gravity anomaly remaining after effects from Units 1 and 2 are removed is a broad north-south-trending low whose major peak lies 5 km north of Sugarloaf Mountain, the largest of the less than 0.3 m.y. old rhyolite domes in the Coso Range. Most of this residual anomaly can be accounted for by a deep, low-density (2.47 g/cm{sup 3}) prismatic body extending from 8 to about 30 km below the surface. While some of this anomaly might be associated with fractured Sierran granitic rocks, its close correlation to a low-velocity zone with comparable geometry suggests that the residual anomaly is probably caused a large zone of partial melt underlying the rhyolite domes of the Coso Range. 12 refs., 9 figs.

  1. Developing an optimally estimated earth gravity model to degree and order 360 from a global set of 30 deg x 30 deg mean surface gravity anomalies

    NASA Astrophysics Data System (ADS)

    Gleason, D. M.

    An optimally estimated earth gravity model (EGM), consisting of a set of geopotential coefficients through a maximum degree and order of 360, has been created from a global set of 259,200 30 deg by 30 deg surface mean gravity anomalies. The model is optimal in the sense that its derivation follows the principles of least-squares collocation which results in the coefficients' error variance/covariance matrix having a minimal trace value. This paper presents: (1) an overview of the mathematical and geodetic principles behind the construction of the model, (2) a discussion on the practical concerns and problems associated with the implementation of these principles on a present-day high speed computer, (3) a brief description of the global 30 deg input mean anomaly file used, (4) an analysis of the statistical properties of the coefficients and their accuracies, and (5) a prognosis for the future.

  2. Gravity-based Identification of Buried Craters with No Topographic Expression

    NASA Astrophysics Data System (ADS)

    Evans, A. J.; Zuber, M. T.

    2013-12-01

    With gravity data acquired by the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft, in conjunction with altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) investigation on the Lunar Reconnaissance Orbiter, we investigate buried craters within the lunar nearside maria. The contrast of low reflectance material of the lunar nearside maria against the high reflectance, anorthositic highlands' crust can be observed from Earth with the naked eye and is arguably one of the most recognizable features of the Moon. Geologic evidence supports the hypothesis that the maria flooded the lunar nearside between 3.8-2.5 Gya, obscuring much of the original physiographic expression of the nearside lowlands, nearly 20% of the entire surface. We use several approaches to visually identify quasi-circular mass anomalies (QCMAs) with minimal or no topographic expression in the free-air gravity and Bouguer anomaly. We identify these anomalies through a systematic search of the lunar nearside in the free-air gravity and Bouguer anomaly maps with shifted and stretched color-scale ranges. Additionally, to reduce identification bias of QCMAs with the largest gravity anomaly contrast and areal extent, we employ gravity gradiometry and antieigenvalues to enhance short-wavelength features in the gravity field. This approach provides a tool to simultaneously examine long- and short-wavelength structures without amplitude bias. Using these methods, we identify over 100 quasi-circular mass anomalies, likely to be ancient impact events, buried by the lunar maria. We use this crater population in conjunction with partially buried craters to investigate the average thickness, volume, and density of maria that have been emplaced on the lunar nearside.

  3. Middle proterozoic tectonic activity in west Texas and eastern New Mexico and analysis of gravity and magnetic anomalies

    SciTech Connect

    Adams, D.C.; Keller, G.R. )

    1994-03-01

    The Precambrian history of west Texas and eastern New Mexico is complex, consisting of four events: Early Proterozoic orogenic activity (16309-1800 Ma), formation of the western granite-rhyolite province (WGRP) (1340-1410 Ma), Grenville age tectonics (1116-1232 Ma), and middle Proterozoic extension possibly related to mid-continent rifting (1086-1109 Ma). Pre-Grenville tectonics, Grenville tectonics, and mid-continent rifting are represented in this area by the Abilene gravity minimum (AGM) and bimodal igneous rocks, which are probably younger. We have used gravity modeling and the comparison of gravity and magnetic anomalies with rock types reported from wells penetrating Precambrian basement to study the AGM and middle Proterozoic extension in this area. The AGM is an east-northeast-trending, 600 km long, gravity low, which extends from the Texas-Oklahoma border through the central basin platform (CBP) to the Delaware basin. This feature appears to predate formation of the mafic body in the CBP (1163 Ma) and is most likely related to Pre-Grenville tectonics, possibly representing a continental margin arc batholith. Evidence of middle Proterozoic extension is found in the form of igneous bodies in the CBP, the Van Horn uplift, the Franklin Mountains, and the Sacramento Mountains. Analysis of gravity and magnetic anomalies shows that paired gravity and magnetic highs are related to mafic intrusions in the upper crust. Mapping of middle Proterozoic igneous rocks and the paired anomalies outlines a 530 km diameter area of distributed east-west-oriented extension. The Debaca-Swisher terrain of shallow marine and clastic sedimentary rocks is age correlative with middle Proterozoic extension. These rocks may represent the lithology of possible Proterozoic exploration targets. Proterozoic structures were reactivated during the Paleozoic, affecting both the structure and deposition in the Permian basin.

  4. Multifractal singular value decomposition (MSVD) for extraction of marine gravity anomaly

    NASA Astrophysics Data System (ADS)

    LYU, Wenchao; Zhu, Benduo; Qiu, Yan

    2015-04-01

    The concept of singularity is used for characterizing different types of nonlinear natural processes, including volcanic eruptions, faults, cloud formation, landslides, rainfall, hurricanes, flooding, earthquakes, wildfires, oil fields and mineralization. The singularity often results in anomalous amounts of energy release or material accumulation within a narrow spatial-temporal interval.The marine gravitation field has multi-fractal features, which show different scale invariant properties in region and local field. The SVD can be used in geophysical data processing for signal and noise separation, radar processing for enhancing weak signals in vertical seismic profiles (VSP). It has also been used in multi component seismic polarization filters and evaluating the amount of wavy reflections in ground-penetrating radar (GPR) images of base surge deposits. With the SVD, a matrix X can be decomposed to a series of eigenvalues. The eigenvalues conformed fractal or multi-fractal distribution described with the power-law function. The multi-fractal SVD can be used for feature extraction and anomaly identification for marine gravity investigation.This paper aims to analyze the marine gravitation data using the SVD and multifractal methods. This paper will also aim to more clearly define the spatial relationship between marine mineralization and the deep geological structures in the field by extracting the marine gravitation information at a particular frequency to provide valuable in depth evidence for predicting new deposits and deep tectonic.

  5. Gravity and fault structures, Long Valley caldera, California

    SciTech Connect

    Carle, S.F.; Goldstein, N.E.

    1987-07-01

    The main and catastrophic phase of eruption in Long Valley occurred 0.73 m.y. ago with the eruption of over 600 km/sup 3/ of rhyolitic magma. Subsequent collapse of the roof rocks produced a caldera which is now elliptical in shape, 32 km east-west by 17 km north-south. The caldera, like other large Quarternary silicic ash-flow volcanoes that have been studied by various workers, has a nearly coincident Bouguer gravity low. Earlier interpretations of the gravity anomaly have attributed the entire anomaly to lower density rocks filling the collapsed structure. However, on the basis of many additional gravity stations and supporting subsurface data from several new holes, a much more complex and accurate picture has emerged of caldera structure. From a three-dimensional inversion of the residual Bouguer gravity data we can resolve discontinuities that seem to correlate with extensions of pre-caldera faults into the caldera and faults associated with the ring fracture. Some of these faults are believed related to the present-day hydrothermal upflow zone and the zone of youngest volcanic activity within the caldera.

  6. Underwater gravity meter survey of San Francisco and San Pablo bays, California, 1982

    USGS Publications Warehouse

    Childs, Jonathan R.; Beyer, L.A.; McCulloch, D.S.; McHendrie, G.A.; Steele, W.C.

    1983-01-01

    Seafloor gravity measurements were made at 281 bottom stations in San Francisco and San Pablo Bays, California, on a series of lines oriented approximately NNE.. Line spacing was approximately 2.8 km and stations along the lines mere spaced 0.5 to 1.5 km apart, between 0.5 and 1.5 km perpendicular to the axis. Sample Bouguer anomalies in the San Francisco Bay range from -15 to +15 mGals (?0.1 mgal), while anomalies in the San Pablo Bay are consistently negative, ranging from +4.0 to -40.0 mGal (?0.2 mGal).

  7. Determining the COB location along the Iberian margin and Galicia Bank from gravity anomaly inversion, residual depth anomaly and subsidence analysis

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Manatschal, Gianreto

    2015-11-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and crustal type are of critical importance in evaluating rifted continental margin formation and evolution. OCT structure, COB location and magmatic type also have important implications for the understanding of the geodynamics of continental breakup and in the evaluation of petroleum systems in deep-water frontier oil and gas exploration at rifted continental margins. Mapping the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust and hence determining the OCT structure and COB location at rifted continental margins is therefore a generic global problem. In order to assist in the determination of the OCT structure and COB location, we present methodologies using gravity anomaly inversion, residual depth anomaly (RDA) analysis and subsidence analysis, which we apply to the west Iberian rifted continental margin. The west Iberian margin has one of the most complete data sets available for deep magma-poor rifted margins, so there is abundant data to which the results can be calibrated. Gravity anomaly inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted continental margins. These quantitative analytical techniques have been applied to the west Iberian rifted continental margin along profiles IAM9, Lusigal 12 (with the TGS-extension) and ISE-01. Our predictions of OCT structure, COB location and magmatic type (i.e. the volume of magmatic addition, whether the margin is `normal' magmatic, magma-starved or magma-rich) have been tested and validated using ODP wells (Legs 103, 149 and 173), which provide

  8. The use of the WGM2012 gravity model to acquire gravimetric data necessary for the reduction of geodetic observations

    NASA Astrophysics Data System (ADS)

    Olszak, Tomasz; Barlik, Marcin

    2014-05-01

    World Gravity Model WGM2012 is the first release of high resolution description inter alia Bouguer and free-air gravity anomaly. It has been created by the Bureau Gravimétrique International (BGI) on base of EGM2008 geopotential model and high resolution topographic model. The poster provides an assessment of the WGM2012 gravity data sources for use in the reduction of geodetic observations. For reductions of geodetic observations onto geoid and ellipsoid (eg. astronomical coordinates, deflections of the vertical, astronomical azimuth and linear measurements) it is necessary a knowledge of the gravity field parameters. Also, in the leveling network it is necessary to collect such information to calculate the normal (or orthometric) correction. The study compared terrestrial data from the Polish National Geological Institute including anomalies and data from the WGM2012 model in the context of using model gravity data to issues related to geodesic reductions.

  9. Crustal structure under the central High Atlas Mountains (Morocco) from geological and gravity data

    NASA Astrophysics Data System (ADS)

    Ayarza, P.; Alvarez-Lobato, F.; Teixell, A.; Arboleya, M. L.; Tesón, E.; Julivert, M.; Charroud, M.

    2005-05-01

    Seismic wide angle and receiver function results together with geological data have been used as constraints to build a gravity-based crustal model of the central High Atlas of Morocco. Integration of a newly acquired set of gravity values with public data allowed us to undertake 2-2.5D gravity modelling along two profiles that cross the entire mountain chain. Modelling suggests moderate crustal thickening, and a general state of Airy isostatic undercompensation. Localized thickening appears restricted to the vicinity of a north-dipping crustal-scale thrust fault, that offsets the Moho discontinuity and defines a small crustal root which accounts for the minimum Bouguer gravity anomaly values. Gravity modelling indicates that this root has a northeasterly strike, slightly oblique to the ENE general orientation of the High Atlas belt. A consequence of the obliquity between the High Atlas borders and its internal and deep structure is the lack of correlation between Bouguer gravity anomaly values and topography. Active buckling affecting the crust, a highly elevated asthenosphere, or a combination of both are addressed as side mechanisms that help to maintain the high elevations of the Atlas mountains.

  10. Evaluation of low-temperature geothermal potential in Utah and Goshen Valleys and adjacent areas, Utah. Part I. Gravity survey

    SciTech Connect

    Davis, D.A.; Cook, K.L.

    1983-04-01

    During 1980 and 1981 a total of 569 new gravity stations were taken in Utah and Goshen Valleys and adjacent areas, Utah. The new stations were combined with 530 other gravity stations taken in previous surveys which resulted in a compilation of 1099 stations which were used in this study. The additional surveys were undertaken to assist in the evaluation of the area for the possible development of geothermal resources by providing an interpreted structural framework by delineating faults, structural trends, intrusions, thickness of valley fill, and increased density of host rock. The gravity data are presented as (1) a complete Bouguer gravity anomaly map with a 2 mgal contour interval on a scale of 1:100,000 and (2) five generally east-trending gravity profiles. A geologic interpretation of the study area was made from the gravity map and from the interpretive geologic cross sections which were modeled along the gravity profiles.

  11. Evidence for Topographic Swells Beneath Gravity Lineations in the South Pacific.

    NASA Astrophysics Data System (ADS)

    Harmon, N.; Forsyth, D. W.; Scheirer, D.

    2004-12-01

    The Gravity Lineations Intraplate Melting Petrologic and Seismologic Expedition (GLIMPSE) experiment is investigating the origins of the gravity lineations in the South Pacific and their relationship to intraplate volcanism at the Sojourn and Hotu Matua ridge systems. Using the satellite free air gravity anomaly and high quality shipboard bathymetry in the GLIMPSE study region, we have calculated the Mantle Bouguer Anomaly (MBA) and the residual Mantle Bouguer Anomaly (rMBA). In the MBA, we see strong negative anomalies (~20-40 mGals) beneath the Sojourn and Brown Ridges as well as beneath the Hotu Matua volcanic complex, indicating low-density material beneath the ridge systems in the form of thickened crust or lower density mantle material. We subtract the effects of surface loading of an elastic plate by the volcanic ridges to find the residual topography and the residual MBA. The residual seafloor topography shows a systematic ~200 km wavelength undulation in the seafloor with a strike roughly parallel to the spreading direction, producing residual bathymetric highs of 100-300 m beneath the Sojourn and Hotu Matua ridge systems. There are broad (100 km wide) negative anomaly bands in the rMBA of ~10-40 mGals beneath the entire length of the Sojourn Ridge to the East Pacific Rise and discontinuously from west of Hotu Matua to the EPR. Similar features are found in the extension of the Puka Puka ridge into the Rano Rahi seamount field. The swells beneath the intraplate volcanism and the gravity lineations require a contribution from subsurface positively buoyant low-density material. The seismic refraction and Rayleigh wave dispersion experiments corroborate the existence of anomalies at depth. The swells contradict lithospheric cracking models of the formation of the gravity lineations that predict the gravity lineations should be located over bathymetric troughs, and favor dynamic models such as small-scale convection.

  12. A New Search for Lunar Mascon Basins using Detrended Kaguya (SELENE) Gravity: Implications for GRAIL

    NASA Astrophysics Data System (ADS)

    Dombard, A. J.; Hauck, S. A.; Balcerski, J.

    2012-12-01

    The collection of GRAIL data and imminent release of its first gravity models will revolutionize understanding of the lunar interior, which motivates an assessment of the current state of knowledge. A primary goal of the GRAIL mission is to understand better mascon basins, large impact craters that display significant positive free-air and Bouguer gravity anomalies. Discovered in a handful of nearside basins during preparations for the Apollo landings and recently expanded by the global Kaguya (SELENE) gravity models, an important question is why is not every large crater a mascon basin, as less than half of the 41 impact basins > 300 km in diameter (minus South Pole-Aitken) have been previously determined to be mascons. An issue not generally considered in the identification of mascons is that the topography, and hence Bouguer gravity, display long-wavelength regional signals that might mask some mascons. Here, we use the SGM100i Kaguya gravity model and LRO's LOLA shape model to examine the free-air, topographic (arising solely from topography), and Bouguer gravity, detrended by omitting the first 5 spherical harmonic degrees from our expansions. In contrast to past studies, we find that most large basins (28 of 41) display characteristics of mascons (e.g., a strong positive Bouguer anomaly generally narrower than the surface rim). Negative annuli surrounding the central highs in the free-air gravity do not exist in the Bouguer gravity, with only 2 definitive exceptions. The fact that the majority of the Bouguer anomalies are narrower than the basin rim and that the negative free-air annulus appears to be a product of the surface topography has implications for the formation of the basins. We propose that beneath a forming large basin, the mantle uplifts in response to the large isostatic imbalance with the transient crater, while the surface topography forms from not only upward but inward collapse of the transient crater's rim wall and adjustment of the melt

  13. Calculation of geoid undulations and gravity anomalies in the South China Sea by using the TOPEX/Poseidon and Geosat altimeter data

    NASA Astrophysics Data System (ADS)

    Zhang, Youguang; Zhang, Jie; Ji, Yonggang; Zhang, Huiqin

    2003-05-01

    In this paper, using TOPEX/Poseidon (9~346cycle) and Geosat/ERM(1~60cycle) altimeter data, the author applies combined adjustment model for calculating the South China Sea geoid undulations after data preprocessing. The difference between calculation result and OSU91A model is 30cm (spatial resolution is 22km). In addition, 12"x12" South China Sea gravity anomalies are calculated by using above geoid data and improved Stokes inverse formula. Contrasted with Scripps Institution of Oceanography gravity anomalies data, the accuracy of computation of gravity anomalies is 12´x10-5m/s2. These computations show that calculation speed is fast and calculation efficiency is high, so the method can calculate rapidly gravity anomalies in special sea area.

  14. Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

    NASA Astrophysics Data System (ADS)

    Sawada, Natsuki; Morota, Tomokatsu; Kato, Shinsuke; Ishihara, Yoshiaki; Hiramatsu, Yoshihiro

    2016-05-01

    Gravity data obtained from the Gravity Recovery and Interior Laboratory have revealed linear gravity anomalies (LGAs) formed by the early global expansion of the Moon and subsequent magma intrusion. In this study, using Lunar Orbiter Laser Altimeter topographic data, we investigated topographic profiles across LGAs to verify that they were formed by extensional tectonics. We found that 17 of the 20 LGAs investigated exhibited a valley structure, suggesting that they were formed by tensile stress. Assuming that these topographic depressions accompanied graben formation, the increase in the lunar radius is estimated to be on the order of several tens of meters. On the other hand, assuming that these topographic depressions accompanied flexure of elastic lithosphere due to the LGA load, the elastic thickness during the LGA formation is estimated as ~10 km. The crater frequencies in the vicinity of LGAs indicate that the peak tectonic activity occurred before the basin-forming epoch.

  15. Mean gravity anomalies from a combination of Apollo/ATS 6 and GEOS 3/ATS 6 SST tracking campaigns. [Satellite to Satellite Tracking

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.; Klosko, S. M.; Wells, W. T.

    1982-01-01

    Advances in satellite tracking data accuracy and coverage over the past 15 years have led to major improvements in global geopotential models. But the spacial resolution of the gravity field obtained solely from satellite dynamics sensed by tracking data is still of the order of 1000 km. Attention is given to an approach which will provide information regarding the fine structure of the gravity field on the basis of an application of local corrections to the global field. According to this approach, a basic satellite to satellite tracked (SST) range-rate measurement is constructed from the link between a ground station, a geosynchronous satellite (ATS 6), and a near-earth satellite (Apollo or GEOS 3). Attention is given to a mathematical model, the simulation of SST gravity anomaly estimation accuracies, a gravity anomaly estimation from GEOS 3/ATS 6 and Apollo/ATS 6 SST observations, and an evaluation of the mean gravity anomalies determined from SST.

  16. Gravity measurements in the vicinity of Georges Bank

    USGS Publications Warehouse

    Hendricks, John D.; Robb, James D.

    1973-01-01

    A total of 97 new bottom gravity measurements on the continental shelf in the vicinity of Georges Bank was reduced to the simple Bouguer anomaly, using a density of 2.80 gm per cm3 for the correction. Results help substantiate the presence of mafic and felsic intrusive bodies along the northern edge of the bank. A gravity low near the center of the bank, trending northeast, corresponds to the Georges Bank trough. An abrupt change in the gravity gradient near the southeast edge of the bank probably represents the thinning of the crust from continental to oceanic thicknesses. Differences in gravity gradient support the suggestion of a fault along the northern edge of the bank.

  17. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements.

    PubMed

    Neumann, Gregory A; Zuber, Maria T; Wieczorek, Mark A; Head, James W; Baker, David M H; Solomon, Sean C; Smith, David E; Lemoine, Frank G; Mazarico, Erwan; Sabaka, Terence J; Goossens, Sander J; Melosh, H Jay; Phillips, Roger J; Asmar, Sami W; Konopliv, Alexander S; Williams, James G; Sori, Michael M; Soderblom, Jason M; Miljković, Katarina; Andrews-Hanna, Jeffrey C; Nimmo, Francis; Kiefer, Walter S

    2015-10-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  18. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements

    PubMed Central

    Neumann, Gregory A.; Zuber, Maria T.; Wieczorek, Mark A.; Head, James W.; Baker, David M. H.; Solomon, Sean C.; Smith, David E.; Lemoine, Frank G.; Mazarico, Erwan; Sabaka, Terence J.; Goossens, Sander J.; Melosh, H. Jay; Phillips, Roger J.; Asmar, Sami W.; Konopliv, Alexander S.; Williams, James G.; Sori, Michael M.; Soderblom, Jason M.; Miljković, Katarina; Andrews-Hanna, Jeffrey C.; Nimmo, Francis; Kiefer, Walter S.

    2015-01-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  19. Gravity anomalies, crustal structure, and seismicity at subduction zones: 1. Seafloor roughness and subducting relief

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble averaging technique is used to remove the long-wavelength topography and gravity field from subduction zones. >200 residual bathymetric and gravimetric anomalies are interpreted within fore arcs, many of which are attributed to the tectonic structure of the subducting plate. The residual-gravimetric expression of subducting fracture zones extends >200 km landward of the trench axis. The bathymetric expression of subducting seamounts with height ≥1 km and area ≥500 km2 (N=36), and aseismic ridges (N>10), is largest near the trench (within 70 km) and above shallow subducting slab depths (SLAB1.0 <17 km). Subducting seamounts are similar in wavelength, amplitude, and morphology to unsubducted seamounts. Morphology, spatial distributions, and reduced levels of seismicity are considered inconsistent with mechanical models proposing wholesale decapitation, and the association of subducting seamounts with large-earthquakes. Subducting aseismic ridges are associated with uplift and steepening of the outer fore arc, a gradual reduction in residual bathymetric expression across the inner fore arc, and a local increase in the width and elevation of the volcanic-arc/orogen. These contrasting expressions reflect the influence of margin-normal variations in rigidity on where and how the upper plate deforms, both to accommodate subducting relief and in response to stresses transmitted across the plate interface. The outer fore arc and arc have lower rigidity due to fracturing and thermal weakening, respectively. Similar associations with complex earthquakes and fault creep suggest aseismic ridge subduction may also be accommodated by the development and evolution of a broad fracture network, the geometrical strength of which may exceed the locking strength of a smooth fault.

  20. Validation of GOCE global gravitational field models by comparison with regional geoid and gravity anomaly surfaces

    NASA Astrophysics Data System (ADS)

    Sprlak, M.; Gerlach, C.; Pettersen, B. R.; Omang, O. C. D.

    2012-04-01

    , the most accurate filtering procedure is applied in validation of real GOCE models. The validation experiment is performed with respect to gravity anomalies and geoid undulations over the territory of Scandinavia.

  1. Integrating stations from the North America Gravity Database into a local GPS-based land gravity survey

    USGS Publications Warehouse

    Shoberg, Thomas G.; Stoddard, Paul R.

    2013-01-01

    The ability to augment local gravity surveys with additional gravity stations from easily accessible national databases can greatly increase the areal coverage and spatial resolution of a survey. It is, however, necessary to integrate such data seamlessly with the local survey. One challenge to overcome in integrating data from national databases is that these data are typically of unknown quality. This study presents a procedure for the evaluation and seamless integration of gravity data of unknown quality from a national database with data from a local Global Positioning System (GPS)-based survey. The starting components include the latitude, longitude, elevation and observed gravity at each station location. Interpolated surfaces of the complete Bouguer anomaly are used as a means of quality control and comparison. The result is an integrated dataset of varying quality with many stations having GPS accuracy and other reliable stations of unknown origin, yielding a wider coverage and greater spatial resolution than either survey alone.

  2. Complete Bouguer gravity map of the Medicine Lake Quadrangle, California

    USGS Publications Warehouse

    Finn, C.

    1981-01-01

    A mathematical technique, called kriging, was programmed for a computer to interpolate hydrologic data based on a network of measured values in west-central Kansas. The computer program generated estimated values at the center of each 1-mile section in the Western Kansas Groundwater Management District No. 1 and facilitated contouring of selected values that are needed in the effective management of ground water for irrigation. The kriging technique produced objective and reproducible maps that illustrated hydrologic conditions in the Ogallala aquifer, the principal source of water in west-central Kansas. Maps of the aquifer, which use a 3-year average, included the 1978-80 water-table altitudes, which ranged from about 2,580 to 3,720 feet; the 1978-80 saturated thicknesses, which ranged from about 0 to 250 feet; and the percentage changes in saturated thickness from 1950 to 1978-80, which ranged from about a 50-percent increase to a 100-percent decrease. A map showing errors of estimate also was provided as a measure of reliability for the 1978-80 water-table altitudes. Errors of estimate ranged from 2 to 24 feet. (USGS)

  3. Regional gravity and magnetic anomalies related to a Proterozoic carbonatite terrane in the eastern Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Denton, K. M.; Ponce, D. A.; Miller, D. M.; Jernigan, C. T.

    2014-12-01

    One of the world's largest rare earth element carbonatite deposits is located at Mountain Pass in the eastern Mojave Desert, California. The 1.4 Ga carbonatite deposit is hosted by and intruded into 1.7 Ga gneiss and schist that occurs in a narrow north-northwest trending belt along the eastern parts of Clark Mountain Range, Mescal Range, and Ivanpah Mountains. The carbonatite is associated with an ultrapotassic intrusive suite that ranges from shonkinite through syenite and granite. Regional geophysical data reveal that the eastern Mojave carbonatite terrane occurs along the northeast edge of a prominent magnetic high and the western margin of a gravity high along the eastern Clark Mountain Range. To improve our understanding of the geophysical and structural framework of the eastern Mojave carbonatite terrane, we collected over 1900 gravity stations and over 600 physical rock property samples to augment existing geophysical data. Carbonatite intrusions typically have distinct gravity, magnetic, and radiometric signatures because these deposits are relatively dense, contain magnetite, and are enriched in thorium or uranium. However, our results show that the carbonatite is essentially nonmagnetic with an average susceptibility of 0.18 x 10-3 SI (n=31) and the associated ultrapotassic intrusive suite is very weakly magnetic with an average susceptibility of 2.0 x 10-3 SI (n=36). Although the carbonatite body is nonmagnetic, it occurs along a steep gradient of a prominent aeromagnetic anomaly. This anomaly may reflect moderately magnetic mafic intrusive rocks at depth. East of the ultrapotassic intrusive rocks, a prominent north trending magnetic anomaly occurs in the central part of Ivanpah Valley. Based on geologic mapping in the Ivanpah Mountains, this magnetic anomaly may reflect Paleoproterozoic mafic intrusive rocks related to the 1.7 Ga Ivanpah Orogeny. Physical property measurements indicate that exposed amphibolite along the eastern Ivanpah Mountains are

  4. Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

    2016-06-01

    An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of

  5. Frozen subduction in the Yangtze block: insights from the deep seismic profiling and gravity anomaly in east Sichuan fold belt

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaosong; Gao, Rui; Wang, Haiyan; Zhang, Jisheng; Guo, Lianghui

    2016-04-01

    The Sichuan basin is the main part of the middle-upper Yangtze block, which has been experienced a long-term tectonic evolution since Archean. The Yangtze block was regarded as a stable block until the collision with the Cathaysia block in late Neoproterozoic. A new deep seismic reflection profile conducted in the eastern Sichuan fold belt (ESFB) discovered a serials of south-dipping reflectors shown from lower crust to the mantle imply a frozen subduction zone within the Yangtze block. In order to prove the speculation, we also obtain the middle-lower crustal gravity anomalies by removing the gravity anomalies induced by the sedimentary rocks and the mantle beneath the Moho, which shows the mid-lower crustal structure of the Sichuan basin can be divided into eastern and western parts. Combined with the geochronology and Aeromagnetic anomalies, we speculated the Yangtze block was amalgamated by the West Sichuan and East Sichuan blocks separated by the Huayin-Chongqing line. The frozen subduction zone subsequently shifted to a shear zone accommodated the lower crustal shortening when the decollement at the base of the Nanhua system functioned in the upper plate.

  6. Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

    NASA Astrophysics Data System (ADS)

    Sun, B.; Wang, L.; Dong, P.; Scientific Team Of Applied Geophysics

    2010-12-01

    The Hailar Basin is one of the most representative basins among the Northeast China Basin Group, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of the Bouguer gravity anomaly, aeromagnetic anomaly as well as petrophysical data, we studied the features of gravity-magnetic fields in the basin and its neighboring areas. A combined approach of Wavelet Multi-scale Decomposition and Power Spectrum Analysis was adopted to quantitatively grade the gravity and magnetic anomalies into four levels. Accordingly, the apparent depths of the source fields can be assessed. The results reveal the crustal density and magnetic structures of the Hailar Basin. Low-order wavelet details of gravity-magnetic anomalies were carried out on studying basin basement structure. Seven major basement faults of the basin were identified, and the basement lithology was discussed and predicted. Three major uplifts and 14 depressions were delineated according to basement depth inversion by the Park method. High-order wavelet approximations of gravity-magnetic anomalies were carried out on studying deep tectonics of the basin. The average Moho depth of the study area is about 40 km, with a mantle uplift located in the northeast of the basin. The average depth of the Curie interface is about 19 km, while the uplift of the Curie interface is in the basin center and its east and west sides are depressions. Finally, inversion of Bouguer gravity anomalies was conducted on an across-basin GGT profile using the Wavelet Multi-scale Decomposition. The inversion results are consistent with those of GGT seismic inversion, suggesting that the Wavelet Multi-scale Decomposition can be applied to distinguish major crustal density interfaces.

  7. Gravity anomaly and geoid undulation results in local areas from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The adjusted GEOS-3 altimeter data, taken as averages within a data frame, have been used to construct free air anomaly and geoid undulation profiles and maps in areas of geophysical interest. Profiles were constructed across the Philippine Trench (at a latitude of 6 deg) and across the Bonin Trench (at a latitude of 28 deg). In the latter case an anomaly variation of 443 mgals in 143 km was derived from the altimeter data. These variations agreed reasonably with terrestrial estimates, considering the predicted point accuracy was about + or - 27 mgals. An area over the Patton Sea mounts was also investigated with the altimeter anomaly field agreeing well with the terrestrial data except for the point directly over the top of the sea mount. It is concluded that the GEOS-3 altimeter data is valuable not only for determining 5 deg and 1 deg x 1 deg mean anomalies, but also can be used to describe more local anomaly variations.

  8. The determination of gravity anomalies from geoid heights using the inverse Stokes' formula, Fourier transforms, and least squares collocation

    NASA Technical Reports Server (NTRS)

    Rummel, R.; Sjoeberg, L.; Rapp, R. H.

    1978-01-01

    A numerical method for the determination of gravity anomalies from geoid heights is described using the inverse Stokes formula. This discrete form of the inverse Stokes formula applies a numerical integration over the azimuth and an integration over a cubic interpolatory spline function which approximates the step function obtained from the numerical integration. The main disadvantage of the procedure is the lack of a reliable error measure. The method was applied on geoid heights derived from GEOS-3 altimeter measurements in the calibration area of the GEOS-3 satellite.

  9. Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble-averaging technique is used to remove the long-wavelength topography and gravity field associated with subduction zones. Short-wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates. A paired (positive-negative) fore-arc anomaly is observed consisting of a long (>1000 km), linear, trench-parallel ridge landward of the deep-sea-terrace basin. Ridges have amplitudes of 1500-3000 m and 160-240 mGal, wavelengths of 150-200 km, and high gravity anomaly to topography ratios (50-75 mGal km-1). The ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in Cascadia, the updip limit of tremor epicenters. The ridge crest may be interpreted as defining the boundary between the velocity-weakening and seismogenic region of the subduction interface and the downdip frictional transition zone. In Tonga-Kermadec, the Kuril Islands and Chile landward ridges are associated with extinct volcanic arcs. Paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of (a) lower crustal underplating beneath the inner fore arc, (b) the transformation of interseismic strain into permanent geologic strain via faulting, folding, or buckling of the inner fore arc, and (c) the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit. Along-strike transitions in fore-arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates. Fore arcs have the added potential of recording the time-integrated response of the upper plate to subduction processes, and fore-arc structure should be considered in tandem with seismological observations.

  10. The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.

    2014-06-01

    The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

  11. Analyzing the Broken Ridge area of the Indian Ocean using magnetic and gravity anomaly maps and geoid undulation and bathymetry data

    NASA Technical Reports Server (NTRS)

    Lazarewicz, A. R.; Sailor, R. V. (Principal Investigator)

    1982-01-01

    A higher resolution anomaly map of the Broken Ridge area (2 degree dipole spacing) was produced and reduced to the pole using quiet time data for this area. The map was compared with equally scaled maps of gravity anomaly, geoid undulation, and bathymetry. The ESMAP results were compared with a NASA MAGSAT map derived by averaging data in two-degree bins. A survey simulation was developed to model the accuracy of MAGSAT anomaly maps as a function of satellite altitude, instrument noise level, external noise model, and crustal anomaly field model. A preliminary analysis of the geophysical structure of Broken Ridge is presented and unresolved questions are listed.

  12. Principal facts for gravity stations in Dixie; Fairview, and Stingaree valleys, Churchill and Pershing counties, Nevada

    USGS Publications Warehouse

    Schaefer, D.H.; Thomas, J.M.; Duffrin, B.G.

    1984-01-01

    During March through July 1979, gravity measurements were made at 300 stations in Dixie Valley, Nevada. In December 1981, 45 additional stations were added--7 in Dixie Valley, 23 in Fairview Valley, and 15 in Stingaree Valley. Most altitudes were determined by using altimeters or topographic maps. The gravity observations were made with a Worden temperature-controlled gravimeter with an initial scale factor of 0.0965 milliGal/scale division. Principal facts for each of the 345 stations are tabulated; they consist of latitude, longitude, altitude, observed gravity, free-air anomaly, terrain correction, and Bouguer anomaly values at a bedrock density of 2.67 grams/cu cm. (Lantz-PTT)

  13. Geoid undulations and gravity anomalies over the Aral Sea, the Black Sea and the Caspian Sea from a combined GEOS-3/SEASAT/GEOSAT altimeter data set

    NASA Technical Reports Server (NTRS)

    Au, Andrew Y.; Brown, Richard D.; Welker, Jean E.

    1991-01-01

    Satellite-based altimetric data taken by GOES-3, SEASAT, and GEOSAT over the Aral Sea, the Black Sea, and the Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulations on a 0.25x0.25 deg. grid and to transform these geoid undulations to free air gravity anomalies. Rapp's 180x180 geopotential model is used as the reference surface for the collocation procedure. The result of geoid to gravity transformation is, however, sensitive to the information content of the reference geopotential model used. For example, considerable detailed surface gravity data were incorporated into the reference model over the Black Sea, resulting in a reference model with significant information content at short wavelengths. Thus, estimation of short wavelength gravity anomalies from gridded geoid heights is generally reliable over regions such as the Black Sea, using the conventional collocation technique with local empirical covariance functions. Over regions such as the Caspian Sea, where detailed surface data are generally not incorporated into the reference model, unconventional techniques are needed to obtain reliable gravity anomalies. Based on the predicted gravity anomalies over these inland seas, speculative tectonic structures are identified and geophysical processes are inferred.

  14. Accuracy of the determination of mean anomalies and mean geoid undulations from a satellite gravity field mapping mission

    NASA Technical Reports Server (NTRS)

    Jekeli, C.; Rapp, R. H.

    1980-01-01

    Improved knowledge of the Earth's gravity field was obtained from new and improved satellite measurements such as satellite to satellite tracking and gradiometry. This improvement was examined by estimating the accuracy of the determination of mean anomalies and mean undulations in various size blocks based on an assumed mission. In this report the accuracy is considered through a commission error due to measurement noise propagation and a truncation error due to unobservable higher degree terms in the geopotential. To do this the spectrum of the measurement was related to the spectrum of the disturbing potential of the Earth's gravity field. Equations were derived for a low-low (radial or horizontal separation) mission and a gradiometer mission. For a low-low mission of six month's duration, at an altitude of 160 km, with a data noise of plus or minus 1 micrometers sec for a four second integration time, we would expect to determine 1 deg x 1 deg mean anomalies to an accuracy of plus or minus 2.3 mgals and 1 deg x 1 deg mean geoid undulations to plus or minus 4.3 cm. A very fast Fortran program is available to study various mission configurations and block sizes.

  15. Comparative study of compensation mechanism of lunar impact basins from new gravity field model of SELENE (Kaguya)

    NASA Astrophysics Data System (ADS)

    Namiki, N.; Sugita, S.; Matsumoto, K.; Goossens, S.; Ishihara, Y.; Noda, H.; Ssasaki, S.; Iwata, T.; Hanada, H.; Araki, H.

    2009-04-01

    The gravity field is a fundamental physical quantity for the study of the internal structure and the evolution of planetary bodies. The most significant problem of the previous lunar gravity models, however, is the lack of direct observations of the far side gravity signals [1]. We then developed a satellite-to-satellite Doppler tracking sub-system for SELENE [2]. In this study, we adopt our new gravity field model with nearly full coverage of the lunar far side to discuss dichotomy of the lunar basins. Because all the nearside impact basins are filled with extensive mare basalt deposits, it is difficult to estimate the subsurface structures, such as uplift of the Moho surface, from gravity measurements. In contrast, far-side impact basins have much less or no mare basalt coverage. This may allow us to investigate the internal structure underneath impact basins. Such knowledge will be important in understanding the response of a solid planetary body to large meteoritic impacts and also the thermal state of the Moon during the late heavy bombardment period. There are distinctive differences between the anomalies of the near side principal mascons and the far side basins. As shown previously [1, 3], the near side principal mascons have sharp shoulders with a gravity plateau and a weakly negative gravity anomaly in the surroundings. In contrast, the far side basins are characterized by concentric rings of positive and negative anomalies. The circular gravity highs agree well with the topographic rims of the basins revealed by SELENE topography model STM-359_grid-02 [4]. In our gravity model, Orientale, Mendel-Rydberg, Lorentz, and Humboldtianum show more affinity with the far side basins than the near side principal mascons [5]. Korolev, Mendeleev, Planck, and Lorentz basins have sharp central peaks of which magnitude in free-air anomalies is almost equivalent to the one in Bouguer anomalies. On the other hand, Orientale, Mendel-Rydberg, Humboldtianum, Moscoviense

  16. Gravity measurements and terrain corrections using a digital terrain model in the NW Himalaya

    NASA Astrophysics Data System (ADS)

    Banerjee, Paramesh

    1998-12-01

    Areas recently gravity surveyed in the NW Himalaya are characterized by high-elevation and high-amplitude topographic undulations. A new method of applying combined Bouguer and terrain corrections using a digital terrain model is highly accurate and offers advantages over conventional techniques by saving efforts and being more flexible. Partitioning parameters for station-dependent inner-zone compartments and station-independent outer zones can be optimally selected for the desired accuracy requirements. A digital terrain database is used to obtain the outer-zone corrections. In the situation of the NW Himalaya surveys, a 1.2 km inner zone is divided into 112 compartments for each station and a digital terrain database containing nearly 16 000 data points for 30″×30″ compartments was applied using the computer program EFFECT.FOR, to compute combined Bouguer and terrain corrections for a 20 km range. The terrain corrections between 20 and 170 km were computed using National Geophysical Data Centre (NGDC) 5'×5' gridded global elevation database. The magnitude of the terrain correction varies between 3 and 50 mGal. The effects of the 20 km range terrain correction are more pronounced on short-medium wavelength anomalies. The Swarghat gravity high is further enhanced while several high-frequency pseudo-anomalies disappear after applying the terrain corrections. The refined Bouguer anomaly varies from -160 mGal at the southern end of the section, to -310 mGal at the northern end, suggesting a Moho depth variation from 45 to nearly 60 km. The steepness of the northward negative gravity gradient, typical for the Himalaya, is considerably reduced after applying a terrain correction for the 170 km range.

  17. Analysis of converted S-waves and gravity anomaly along the Aegir Ridge: implications for crustal lithology

    NASA Astrophysics Data System (ADS)

    Rai, A. K.; Breivik, A. J.; Mjelde, R.; Hanan, B. B.; Ito, G.; Sayit, K.; Howell, S.; Vogt, P. R.; Pedersen, R.

    2012-12-01

    The Aegir Ridge is an extinct spreading ridge in North-East Atlantic ocean. A thinner than normal crust around the Aegir Ridge appears as a hole in the extensively magmatic surroundings. Its proximity to the Iceland hot-spot makes it particularly important for understanding the changing dynamics of hotspot-ridge interaction. An integrated seismic and dredging experiment was conduced during the summer of 2010 with the primary aim to understand the nature of magmatism along the ridge shortly before cessation of seafloor spreading through variations of sub-seafloor lithological properties. Here, we present results of analysis of converted shear-waves recorded on OBS-sesimic data, and ship-gravity data. The shear-wave study enables us to quantify the variation of Vp/Vs in the sediments, crust and the upper-most mantle. We also inverted the gravity data to determine the sub-seafloor density distribution. The P- to S- converted shear-waves were identified on 20 OBSs along a profile with a total length of 550 km parallel to the ridge-axis. The sedimentary section on top of the crystalline crust is well illuminated in the streamer data. The forward modelling of the OBS data reveals that the Vp/Vs ratio in sediments are as high as 4.8, decreasing rapidly to a value of 3.00, primarily due to compaction of sediments with depth. Identification of sufficient PnS and PSn phases enable us to model the crustal and upper-most mantle Vp/Vs. The upper crystalline crust requires a Vp/Vs value of 1.99 and 1.89 for the southern and the northern profiles respectively, to fit the observations. The lower crust and upper-most part of the mantle have a Vp/Vs of ~1.82 and 1.795 respectively. Slightly lower Vp and moderate increase in Vp/Vs in parts of the crust and upper mantle presumably indicate presence of faulting, fracturing in the crust and moderate degree of serpentinization of the upper mantle. A sub-seafloor density model is derived by non-linear inversion of the gravity anomaly. The

  18. Dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, estimated by eigenvectors of gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Kusumoto, Shigekazu

    2016-09-01

    We estimated the dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, by using the dip of the maximum eigenvector of the gravity gradient tensor. A series of earthquakes in Kumamoto and Oita beginning on 14 April 2016 occurred along this tectonic line, the largest of which was M = 7.3. Because a gravity gradiometry survey has not been conducted in the study area, we calculated the gravity gradient tensor from the Bouguer gravity anomaly and employed it to the analysis. The general dip distribution of the Oita-Kumamoto Tectonic Line was found to be about 65° and tends to be higher towards its eastern end. In addition, we estimated the dip around the largest earthquake to be about 60° from the gravity gradient tensor. This result agrees with the dip of the earthquake source fault obtained by Global Navigation Satellite System data analysis.[Figure not available: see fulltext.

  19. Use of gravity potential field methods for defining a shallow magmatic intrusion: the Mt. Amiata case history (Tuscany, Central Italy)

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Rinaldo Barchi, Massimiliano; Pauselli, Cristina; Heyde, Ingo

    2016-04-01

    We analyzed the Bouguer gravity anomaly signal beneath the Mt. Amiata area in order to reconstruct the subsurface setting. The study area is characterized by a pronounced gravity minimum, possibly correlated with the observed anomalous heat flow and hydrothermal activity. Using different approaches, previous authors defined a low density body (generally interpreted as a magmatic intrusion) beneath this area, which could explain the observed gravity anomaly minimum. However the proposed geologic models show different geometries and densities for the batholith. The gravity data used in this study (kindly provided by eni) were acquired from different institutions (eni, OGS, USDMA and Servizio Geologico d'Italia) and collected in a unique dataset, consisting of about 50000 stations, randomly distributed, which cover Central Italy, with a spacing of less than 1 km. For each station the elevation and the Bouguer gravity anomaly data are given. From this dataset, we created two maps of the Bouguer gravity anomaly and the topography, using the Minimum Curvature gridding method considering a grid cell size of 500m x 500m. The Bouguer gravity anomaly has been computed using a density of 2.67 g/cm3. From these maps we extracted a window of about 240 km2 (12x20 km) for the study area, which includes the Mt. Amiata region and the adjacent Radicofani sedimentary basin. The first part of this study was focused on calculating the first order vertical derivative and the power spectra analysis of the Bouguer gravity anomaly to enhance the effect of shallow bodies and estimating the source depth respectively. The second part of this study was focused on constructing a 3D geological density model of the subsurface setting of the studied area, implementing a forward modelling approach. The stratigraphy of the study area's upper crust schematically consists of six litho-mechanical units, whose density was derived from velocity data collected by active seismic surveys. A preliminary

  20. Analysis of gravimetric anomalies in Furnas caldera (São Miguel, Azores)

    NASA Astrophysics Data System (ADS)

    Montesinos, F. G.; Camacho, A. G.; Vieira, R.

    1999-09-01

    Furnas Volcano (São Miguel Island, Azores) is a steep-sided caldera complex resulting from several collapses. In this paper, we analyse and interpret the gravity survey carried out by the Instituto de Astronomı´a y Geodesia (Spain) and the gravity data published by the Instituto Nacional de Meteorologia e Geofisica (Portugal). The resulting Bouguer anomaly reveals the presence of a regional trend, several local features and a component of noise. In separating the regional trend we use a robust polynomial fitting. Further, a covariance analysis and a least squares prediction are applied to filter the noise and to model the local anomaly. A first signal map represents the main local anomaly, while the secondary signal map shows superficial anomalies. This distribution reveals a local main minimum close to the 1630 A.D. and Gaspar craters. Several possible alignments are shown that lead to a model, mainly with SW-NE and SE-NW orientations, of the negative anomaly, with the pattern of the low density zones showing a relationship with the volcanic features. Applying a stabilized linear method of gravimetric inversion, we obtain a density contrast distribution of the sources of the filtered local Bouguer anomaly, considering as unknowns the anomalous densities of a fixed discrete distribution of rectangular prisms which represents the subsoil volume. A mixed minimization criteria for the weighted residuals and the weighted density contrast allow us to obtain a solution as a discrete three-dimensional density contrast model. The obtained anomalous densities model shows a clear relation with the structure of the caldera complex and tectonic trends, with the principal body of negative contrast density being associated with the subsurface structure of the caldera.

  1. Detailed gravity and aeromagnetic surveys in the Black Rock Desert Area, Utah. Topical report

    SciTech Connect

    Serpa, L.F.; Cook, K.L.

    1980-01-01

    Aeromagnetic and gravity surveys were conducted during 1978 in the Black Rock Desert, Utah over an area of about 2400 km/sup 2/ between the north-trending Pavant and Cricket Mountains. The surveys assisted in evaluating the geothermal resources in the Meadow-Hatton Known Geothermal Resource Area (KGRA) and vicinity by delineating geophysical characteristics of the subsurface. The gravity measurements from approximately 700 new stations were reduced to complete Bouguer gravity anomaly values with the aid of a computerized terrain-correction program and contoured at an interval of 1 milligal. The aeromagnetic survey was drape flown at an altitude of 305 m (1000 ft) and a total intensity residual aeromagnetic map with a contour interval of 20 gammas was produced. Two gravity and aeromagnetic east-west profiles and one north-south profile were modeled using a simultaneous 2 1/2-dimensional modeling technique to provide a single model satisfying both types of geophysical data.

  2. Application of high-pass filtering techniques on gravity and magnetic data of the eastern Qattara Depression area, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Zahra, Hesham Shaker; Oweis, Hesham T.

    2016-06-01

    In this work, a reconnaissance study is presented to delineate the subsurface tectonics and lithological inferences of the eastern area of Qattara Depression using the Bouguer gravity and aeromagnetic data. To achieve this goal, several transformation techniques and filtering processes are accomplished on these maps. At first, the total intensity aeromagnetic map is processed through the application of reduction to the magnetic north pole technique. The fast Fourier transform is carried out on the gravity and RTP magnetic data for establishing and defining the residual (shallow) sources. The frequency high-pass filtering is used to enhance the anomaly wavelengths associated with the shallow sources. The used processing techniques are the polynomial surface fitting enhancement, Laplacian, Strike Filtering, Enhancement Utilization, Suppression Utilization, Butterworth Filtering Utilization, Butterworth high-pass filter, Euler's deconvolution and forward modeling. The equivalent depths of the isolated short wavelength anomalies are 0.759 and 0.340 km below the flight surface, and the depths of the intermediate wavelength anomalies are 1.28 and 2.00 km for the gravity and magnetic data, respectively. Finally, the quantitative interpretations of the Bouguer gravity and RTP magnetic maps of the study area, reflect the occurrence of the various types of structures and their components. The main tectonic deformations of the study area have NNW-SSE, NNE-SSW, NE-SW, NW-SE and E-W trends.

  3. Gravity gradient for Greenland and its tectonic interpretation

    NASA Astrophysics Data System (ADS)

    Grushinsky, Andrew N.

    2013-04-01

    Gravity gradient is the indicator of the stress conditions in the lithosphere. The axis of gradient signs changing indicates the boundary of blocks exposed to different tensions. The lines of maxima and minima of gravity gradient correspondingly marked the boundary of zones of compression and expansion. Four various types of the gravity anomalies was calculated: in free air, Bouguer's, Glennie's and isostatic. And then was calculated their gradients. The preliminary analysis of gradients shows, that its qualitative behavior for all types of gravity anomalies is very closely and, therefore, conclusions about the stress conditions in the lithosphere of the considering region are definite. Range of the changing for gradients of gravity in free air anomalies - from -96.1 to 135.8 eötvös, and for gradients of gravity Bouguer's anomalies - from -122.6 to 141.9 eötvös. Range of the changing for gradients of gravity Glennie's and isostatic anomalies are substantially smaller, for gradients of gravity Glennie's anomalies - from -27.6 to 25.5 eötvös, and for gradients of gravity isostatic anomalies - from -19.2 to 21.2 eötvös. This difference in the gradient values, evidently, connects with the difference in the thoroughness and the degree of averaging of the anomalies. Analysis of gravity gradient shown the following: 1. In the western part of the researching region are distinguished three linear structures (two maxima and one minimum), which marked rift zone of the Baffin Bay and Davis Strait. This disappeared rift characterized by depressed zone, lengthened from Nares strait along the west sea coast of Greenland. In the south part of this zone localized deep fault, which northward become lesser expressed. To the north and north-east from the Nares strait lengthened to the North Pole zone of compression, blocked up existing previously rift, by which the rotation of the Greenland part of Canadian shield from its cardinal part happened. Center of this rotation

  4. Structure of the midcontinent basement. Topography, gravity, seismic, and remote sensing

    NASA Technical Reports Server (NTRS)

    Guinness, E. A.; Strebeck, J. W.; Arvidson, R. E.; Scholz, K.; Davies, G. F.

    1981-01-01

    Some 600,000 discrete Bouguer gravity estimates of the continental United States were spatially filtered to produce a continuous tone image. The filtered data were also digitally painted in color coded form onto a shaded relief map. The resultant image is a colored shaded relief map where the hue and saturation of a given image element is controlled by the value of the Bouguer anomaly. Major structural features (e.g., midcontinent gravity high) are readily discernible in these data, as are a number of subtle and previously unrecognized features. A linear gravity low that is approximately 120 to 150 km wide extends from southeastern Nebraska, at a break in the midcontinent gravity high, through the Ozark Plateau, and across the Mississippi embayment. The low is also aligned with the Lewis and Clark lineament (Montana to Washington), forming a linear feature of approximately 2800 km in length. In southeastern Missouri the gravity low has an amplitude of 30 milligals, a value that is too high to be explained by simple valley fill by sedimentary rocks.

  5. Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Griscom, A.; Jachens, R.C.

    1989-01-01

    Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. -from Authors

  6. Spherical-earth gravity and magnetic anomaly modeling by Gauss-Legendre quadrature integration

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J.

    1981-01-01

    Gauss-Legendre quadrature integration is used to calculate the anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical earth. The procedure involves representation of the anomalous source as a distribution of equivalent point gravity poles or point magnetic dipoles. The distribution of equivalent point sources is determined directly from the volume limits of the anomalous body. The variable limits of integration for an arbitrarily shaped body are obtained from interpolations performed on a set of body points which approximate the body's surface envelope. The versatility of the method is shown by its ability to treat physical property variations within the source volume as well as variable magnetic fields over the source and observation surface. Examples are provided which illustrate the capabilities of the technique, including a preliminary modeling of potential field signatures for the Mississippi embayment crustal structure at 450 km.

  7. Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (Principal Investigator)

    1981-01-01

    The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

  8. Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, J.; Maldonado, A.; Schreider, A. A.

    2003-06-01

    The main features of the deep structure of the Gorringe Ridge are analysed on the basis of gravity and magnetic measurements, as well as seismic profiles, drill holes, rock dredges, submersible observations and seismicity data. The gravity and magnetic models of the Gettysburg and Ormonde seamounts, which form the Gorringe Ridge, suggest that the Moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold. This structure is the result of a northwestward vergent thrust that deformed the oceanic crust, with a minimum slip of approximately 20 km. The activity of the thrust probably started 20 Myr, and produced the recent stages of seamount uplift. The seamount is mainly composed of gabbros of the oceanic crust, serpentinized rocks and alkaline basalts. The large antiform, located in the hangingwall of the thrust, is probably deformed by minor faults. This oceanic ridge is a consequence of the oblique convergence between the African Plate and the overlapping Eurasian Plate.

  9. Three-dimensional density interface inversion of gravity anomalies in the spectral domain

    NASA Astrophysics Data System (ADS)

    Feng, Juan; Meng, Xiaohong; Chen, Zhaoxi; Zhang, Sheng

    2014-06-01

    Based on the Fourier transform, the Parker-Oldenburg algorithm in the frequency domain was extended for the three-dimensional case where the density changes with depth. From this, a gravity interface inversion formula was derived in which the assumed density can be varied laterally and vertically. Iterative convergence is assured by fixing a particular depth as the datum plane below the surface to reduce the interface fluctuation. The results of an example set of synthetic gravity data indicate that the proposed method gives high precision and rapid convergence, with high practical value for the inversion of density interfaces. This method was also used to determine the Moho depth beneath northern China. The results were confirmed by seismic sounding data. Differences between seismic sounding data and inverted depth were insignificant and were in the range of -0.92-1.67 km.

  10. Improved global prediction of 300 nautical mile mean free air anomalies

    NASA Technical Reports Server (NTRS)

    Cruz, J. Y.

    1982-01-01

    Current procedures used for the global prediction of 300nm mean anomalies starting from known values of 1 deg by 1 deg mean anomalies yield unreasonable prediction results when applied to 300nm blocks which have a rapidly varying gravity anomaly field and which contain relatively few observed 60nm blocks. Improvement of overall 300nm anomaly prediction is first achieved by using area-weighted as opposed to unweighted averaging of the 25 generated 60nm mean anomalies inside the 300nm block. Then, improvement of prediction over rough 300nm blocks is realized through the use of fully known 1 deg by 1 deg mean elevations, taking advantage of the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations inside the 300nm block. An improved prediction model which adapts itself to the roughness of the local anomaly field is found to be the model of Least Squares Collocation with systematic parameters, the systematic parameter being the slope b which is a type of Bouguer slope expressing the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations.

  11. Lithology identification with gravity and magnetic anomalies for mine exploration in the China-Mongolia border

    NASA Astrophysics Data System (ADS)

    Meng, X.; Wang, J.

    2015-12-01

    China-Mongolia border is an important metallogenic province, its structural is complex and the study of it is of great significance for future detecting. In the last three years, we have conducted gravity and magnetic survey in the eastern segment of the China-Mongolia border along the profile, hoping to get a detailed characterization of the subsurface of this area. In this study, we conducted lithology identification in this area with measured gravity and magnetic data. In our work, topological calculations were performed on inversion data and physical property data for lithology identification. Our work can be summarized into the following steps: Firstly, the rock density and magnetic susceptibility near the survey profiles were summarized by field reconnaissance, and the lithology was divided into several types. Thus, a correspondence between lithology and physical properties was defined to some extent. Secondly, different mapping equations were established according to the physical properties for each lithology.Then, inversion of the gravity and magnetic data have been performed to get the physical properties (density and susceptibility) below the profile. Lastly, the lithology was identified through gravity and magnetic inversion result and the mapping equations mentioned above. In our study, the magmatic rocks within 50 km of the lower half space can be divided into four major types based on the identification result. The lithology varies significantly from north to south below this profile. Moreover, the lithology distribution trend and the formation age of the lower half space is summarized based on characteristics of the gravity and magnetic fields and the tectonic setting. For lithology identification with different types of data, we think that identify lithology information by one of the data can be conducted firstly, such as magnetic susceptibility, and then bring the results to lithology identification among the inversion of other data , which greatly

  12. On Different Techniques for the Calculation of Bougher Gravity Anomalies for Joint Inversion of Geophysical Data in the Rio Grande Rift

    NASA Astrophysics Data System (ADS)

    Zamora, A.; Hussein, M. J.; Velasco, A. A.

    2012-12-01

    Density variations in the Earth result from different material properties, which reflect the tectonic processess attributed to a region. Density variations can be identified through measurable material properties, such as seismic velocities, gravity field, magnetic field, etc. Gravity anomaly inversions are particularly sensitive to density variations but suffer from significant non-uniqueness. However, using inverse models with gravity Bougher anomalies and other geophysical data, we can determine three dimensional structural and geological properties of the given area. We explore different techniques for the calculation of Bougher gravity anomalies for their use in joint inversion of multiple geophysical data sets. Various 2- and 3-Dimensional (3-D) gravity profile forward modeling programs have been developed as variations of existing algorithms; these variations have similarities, differences, and strengths and weaknesses. The purpose of this study is to determine the most effective gravity forward modeling method that can be used to combine the information provided by complementary datasets, such as gravity and seismic information, to improve the accuracy and resolution of Earth models obtained for the underlying structure of the Rio Grande Rift. In an effort to determine the most appropriate method to use in a joint inversion algorithm and a data fusion approach currently in development, we test each approach by using a model of the Rio Grande Rift obtained from seismic surface wave dispersion and receiver functions. We find that there are different uncertainties associated with each methodology that affect the accuracy achieved by including gravity profile forward modeling. Moreover, there exists a bigger margin of error associated to the 2-D methods due to the simplification of calculations that do not take into account the 3-D characteristics of the Earth's structure.

  13. Geophysical investigations on the gravity and aeromagnetic anomalies of the region between Sapanca and Duzce, along the North Anatolian Fault, Turkey

    NASA Astrophysics Data System (ADS)

    Tigli, Cigdem Sendur; Ates, Abdullah; Aydemir, Attila

    2012-12-01

    In this paper, it is aimed to model subsurface structures to the east of the Gulf of Izmit through Duzce by using the gravity and aeromagnetic anomaly data. 1/500.000 scaled gravity anomaly map of the area was taken from the General Directorate of Mineral Research and Exploration (MTA) and it was digitized. The aeromagnetic anomaly data were obtained in the digital form. 3D and 2D models were constructed to reveal the subsurface structure in two different inset regions in the study area including most important negative and positive gravity anomalies. Seismic velocities obtained from the deep seismic recordings were converted to densities. In addition, density information from a previous research was also taken. These densities were used for construction of 3D and 2D gravity models where it was shown that there are narrow and long sedimentary basins and depressions with 0.5-3 km depths. These sedimentary basins with the shape of negative flower structures indicating pull-apart basins are controlled by the active fault segments of the North Anatolian Fault (NAF). Earthquake epicenter data were also correlated with the constructed models from the gravity anomalies. Positive gravity anomalies are also caused by very shallow (about 2 km) masses that are accepted as the crustal origin intrusions into the fractures of the NAF and, ophiolites and gabbro outcropping on the surface of the studied regions. These intrusives and remnants of the Tethys Ocean are located between the fault segments where the fault bifurcates and they also constitute barriers for straight extension of the NAF. Analytic signal method was applied to the aeromagnetic anomaly data to determine the locations and boundaries of the causative bodies. Those bodies are observed around Duzce, and to the E-SE of it, to the NW of Golyaka and a large mass between Adapazari and Sapanca. Shallow settlement of these magmatics was confirmed by the second vertical derivative of the aeromagnetic data. An anti

  14. Calculation of Moho Depth by Gravity Anomalies in Qinghai-Tibet Plateau Based on an Improved Iteration of Parker-Oldenburg Inversion

    NASA Astrophysics Data System (ADS)

    Zhang, Chong; Huang, Danian; Wu, Guochao; Ma, Guoqing; Yuan, Yuan; Yu, Ping

    2015-10-01

    A derivative formula for interface inversion using gravity anomalies, combining the Parker-Oldenburg method for calculating and inverting gravity anomalies with Xu's iteration method for continuing potential fields, leads to a convergent inversion algorithm and an optimally located density interface geometry. In this algorithm, no filtering or any other convergence control techniques are needed during iteration. The method readily iterates the variable depth of the gravity interface by means of upward continuation in a form equivalent to inversion iteration in the Fourier domain instead of the divergent, downward continuation term. This iteration algorithm not only efficiently solves the divergence problem in the inversion iteration procedure but also validly obtains an excellent result for the density interface. A numerical example is presented to illustrate perfect execution of this approach in gravity exploration, and a real geophysical example of inversion of the Moho depth by means of this approach using a set of measured gravity anomalies over the Qinghai-Tibet Plateau in China is offered.

  15. New gravity and magnetics map of eastern part of Azores

    NASA Astrophysics Data System (ADS)

    Dehghani, A.

    2013-12-01

    The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

  16. New gravity and magnetics map of eastern part of Azores

    NASA Astrophysics Data System (ADS)

    Dehghani, Ali

    2014-05-01

    The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

  17. Downward continuation of the free-air gravity anomalies to the ellipsoid using the gradient solution and terrain correction: An attempt of global numerical computations

    NASA Technical Reports Server (NTRS)

    Wang, Y. M.

    1989-01-01

    The formulas for the determination of the coefficients of the spherical harmonic expansion of the disturbing potential of the earth are defined for data given on a sphere. In order to determine the spherical harmonic coefficients, the gravity anomalies have to be analytically downward continued from the earth's surface to a sphere-at least to the ellipsoid. The goal is to continue the gravity anomalies from the earth's surface downward to the ellipsoid using recent elevation models. The basic method for the downward continuation is the gradient solution (the g sub 1 term). The terrain correction was also computed because of the role it can play as a correction term when calculating harmonic coefficients from surface gravity data. The fast Fourier transformation was applied to the computations.

  18. Preliminary gravity investigations of the Wahmonie Site, Nevada Test Site, Nye County, Nevada

    SciTech Connect

    Ponce, D.A.

    1981-12-31

    A gravity survey of the southwest corner of the Nevada Test Site was completed during 1979 to 1980 as part of an effort to characterize a possible radioactive waste storage site in granitic rocks. The survey outlined a large, broad, and flat gravity high centered near Wahmonie Site. Combined geophysical data indicate that the anomalous area is underlain by a dense, magnetic, and possibly intrusive body. Gravity data show a +15 milligal Bouguer anomaly coincident with a large positive aeromagnetic anomaly. The data reveal a prominent fault at the west edge of the inferred intrusive. Both gravity and magnetic anomalous highs extend NNE over a horst composed predominantly of rhyodacite of the Tertiary Salyer Formation. Local aeromagnetic highs are closely associated with two granodiorite exposures on the eastern edge of the horst. A local gravity high of about +2 milligal is centered directly over the southern granodiorite exposure and another high is centered over the northern exposure. A steep gravity gradient outlining the gravity high coincides with the outer edge of a zone of hydrothermal alteration which surrounds the horst. The gravity gradient probably marks the approximate limit of an intrusive body.

  19. Structure of the southern Rio Grande rift from gravity interpretation

    NASA Astrophysics Data System (ADS)

    Daggett, P. H.; Keller, G. R.; Wen, C.-L.; Morgan, P.

    1986-05-01

    Regional Bouguer gravity anomalies in southern New Mexico have been analyzed by two-dimensional wave number filtering and poly-nomial trend surface analysis of the observed gravity field. A prominent, regional oval-shaped positive gravity anomaly was found to be associated with the southern Rio Grande rift. Computer modeling of three regional gravity profiles suggests that this anomaly is due to crustal thinning beneath the southern Rio Grande rift. These models indicate a 25 to 26-km minimum crustal thickness within the rift and suggest that the rift is underlain by a broad zone of anomalously low-density upper mantle. The southern terminus of the anomalous zone is approximately 50 km southwest of El Paso, Texas. A thinning of the rifted crust of 2-3 km relative to the adjacent Basin and Range province indicates an extension of about 9 percent during the formation of the modern southern Rio Grande rift. This extension estimate is consistent with estimates from other data sources. The crustal thinning and anomalous mantle is thought to result from magmatic activity related to surface volcanism and high heat flow in this area.

  20. Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.

    USGS Publications Warehouse

    Cady, J.W.

    1980-01-01

    An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross‐section and finite strike‐length. The equation can be separated into the two‐dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term “two‐and‐a‐half dimensional” (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.

  1. A new automatic method for estimation of magnetization and density contrast by using three-dimensional (3D) magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Bektas, Ozcan; Ates, Abdullah; Aydemir, Attila

    2012-09-01

    In this paper, a new method estimating the ratio of magnetic intensity to density contrast of a body that creates magnetic and gravity anomalies is presented. Although magnetic intensity and density of an anomalous body can be measured in the laboratory from the surface samples, the proposed new method is developed to determine the magnetic intensity and density contrast from the magnetic and gravity anomalies when the surface samples are not available. In this method, density contrast diagrams of a synthetic model are produced and these diagrams are prepared as graphics where the magnetic intensity (J) is given in the vertical axis and Psg (pseudogravity)/Grv (gravity) values in horizontal axis. The density contrast diagrams can be prepared as three sub-diagrams to show the low, middle and high ranges allowing obtain density contrast of body. The proposed method is successfully tested on the synthetic models with and without error. In order to verify the results of the method, an alternative method known as root-mean-square (RMS) is also applied onto the same models to determine the density contrast. In this manner, maximum correlation between the observed gravity and calculated gravity anomalies is searched and confirmation of the results is supported with the RMS method. In order to check the reliability of the new method on the field data, the proposed method is applied to the Tetbury (England) and Hanobasi (Central Turkey) magnetic and gravity anomalies. Field models are correlated with available geological, seismic and borehole data. The results are found consistent and reliable for estimating the magnetic intensity and density contrast of the causative bodies.

  2. Preliminary isostatic residual gravity anomaly map of Paso Robles 30 x 60 minute quadrangle, California

    USGS Publications Warehouse

    McPhee, D.K.; Langenheim, V.E.; Watt, J.T.

    2011-01-01

    This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in the central California Coast Ranges and will serve as a basis for modeling the shape of basins and for determining the location and geometry of faults within the Paso Robles quadrangle. Local spatial variations in the Earth\\'s gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithological or structural boundaries. High-density rocks exposed within the central Coast Ranges include Mesozoic granitic rocks (exposed northwest of Paso Robles), Jurassic to Cretaceous marine strata of the Great Valley Sequence (exposed primarily northeast of the San Andreas fault), and Mesozoic sedimentary and volcanic rocks of the Franciscan Complex [exposed in the Santa Lucia Range and northeast of the San Andreas fault (SAF) near Parkfield, California]. Alluvial sediments and Tertiary sedimentary rocks are characterized by low densities; however, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of older basement rocks.

  3. Gravity field of Kuwait and its relevance to major geological structures

    SciTech Connect

    Warsi, W.E.K. )

    1990-10-01

    Regional gravity surveys were done in the state of Kuwait during 1986-1988. The new gravity maps show a good correlation with geomorphological features as well as with deeper geological structures. The free-air anomaly map clearly reflects the topography of the Jal Az Zor and Ahmadi ridges, and Wadi Al-Batin. The Bouguer anomaly map is dominated by two prominent gravity highs correlatable with subsurface structural arches. The north-trending gravity high in eastern Kuwait represents the effect of a major structure, the Kuwait arch, along which many important oil fields are located. A smaller northwest-trending high mapped in western Kuwait indicates the presence of a second subsurface arch, which in this paper is named the Dibdibba arch. The two gravity highs are separated by a wedge-shaped gravity low presumably caused by thicker sediments of the Dibdibba basin. Magnetic measurements along selected profiles show the two arches to be associated with 100-200-nT (nannotesla) anomalies apparently reflecting the positive subsurface relief of the crystalline basement. Along the length of the Kuwait arch, magnetic data also indicate lateral susceptibility variations possibly related to lithological variations within the basement.

  4. On the gravitational potential and field anomalies due to thin mass layers

    NASA Technical Reports Server (NTRS)

    Ockendon, J. R.; Turcotte, D. L.

    1977-01-01

    The gravitational potential and field anomalies for thin mass layers are derived using the technique of matched asymptotic expansions. An inner solution is obtained using an expansion in powers of the thickness and it is shown that the outer solution is given by a surface distribution of mass sources and dipoles. Coefficients are evaluated by matching the inner expansion of the outer solution with the outer expansion of the inner solution. The leading term in the inner expansion for the normal gravitational field gives the Bouguer formula. The leading term in the expansion for the gravitational potential gives an expression for the perturbation to the geoid. The predictions given by this term are compared with measurements by satellite altimetry. The second-order terms in the expansion for the gravitational field are required to predict the gravity anomaly at a continental margin. The results are compared with observations.

  5. Isostasy, Stress and Gravitational Potential Energy in the Southern Atlantic - Insights from Satellite Gravity Observations

    NASA Astrophysics Data System (ADS)

    Goetze, H. J.; Klinge, L.; Scheck-Wenderoth, M.; Dressel, I.; Sippel, J.

    2015-12-01

    New satellite gravity fields e.g. EGM2008, GoCo3S and very recently EIGEN-6C4 (Förste et al., 2014) provide high-accuracy and globally uniform information of the Earth's gravity field and partly of its gradients. The main goal of this study is to investigate the impact of this new gravity field and its processed anomalies (Bouguer, Free-air and Vening-Meinesz residual fields) on lithospheric modelling of passive plate margins in the area of the Southern Atlantic. In an area fixed by the latitudes 20° N - 50° S and longitudes 70° W - 20° E we calculated station-complete Bouguer anomalies (bathymetry/topography corrected) both on- and offshore and compared them with the gravity effect of a velocity model which bases on S - waves tomography (Schaeffer and Lebedev, 2013). The corresponding maps provide more insight in the abnormal mass distribution of oceanic lithosphere and the ocean-continent transition zones on both sides of the Atlantic Ocean than Free-air anomalies which are masked by bathymetry. In a next step we calculated isostatic residual fields (Vening-Meinesz isostasy with regard to different lithospheric rigidities) to remove global components (long wavelengths) from the satellite gravity. The Isostatic residual field will be compared with the GPE (gravitational potential energy). GPE variations in the Southern Atlantic, relative to the reference state, were calculated as ΔGPE. Often the oceanic lithosphere is characterized by negative ∆GPE values indicating that the ocean basin is in compression. Differences from this observation will be compared with the state of stress in the area of the passive margins of South America and South Africa and the oceanic lithosphere in between. Schaeffer, A. J. and S. Lebedev, Global shear-speed structure of the upper mantle and transition zone. Geophys. J. Int., 194 (1), 417-449, 2013. doi:10.1093/gji/ggt095

  6. Geologic structure of the northern New Caledonia ridge, as inferred from magnetic and gravity anomalies

    USGS Publications Warehouse

    Collot, J.-Y.; Rigolot, P.; Missegue, F.

    1988-01-01

    Bathymetric, gravity, and magnetic data collected in the southwest Pacific Ocean over the northern New Caledonia ridge show that the main geological units known from the island of New Caledonia extend northward from this island, beneath the Grand Lagon Nord, the Grand Passage, and the d'Entrecasteaux reefs. These data support the model of tectonic evolution of the New Caledonia region proposed by Kroenke (1984). Differences in structure, geophysical signatures and morphology evident between areas north and those south of the Grand Passage, together with the nearness of the Le Noroit massif west of the Grand Passage, suggest that contemporaneously with Eocene to early Oligocene subduction along the western New Caledonia margin, an arc-ridge collision may have occurred near the northern termination of this subduction zone. -from Authors

  7. The alpine Swiss-French airborne gravity survey

    NASA Astrophysics Data System (ADS)

    Verdun, Jérôme; Klingelé, Emile E.; Bayer, Roger; Cocard, Marc; Geiger, Alain; Kahle, Hans-Gert

    2003-01-01

    In February 1998, a regional-scale, airborne gravity survey was carried out over the French Occidental Alps within the framework of the GéoFrance 3-D research program.The survey consisted of 18 NS and 16 EW oriented lines with a spacing of 10 and 20 km respectively, covering the whole of the Western French Alps (total area: 50 000 km2; total distance of lines flown: 10 000 km). The equipment was mounted in a medium-size aircraft (DeHavilland Twin Otter) flowing at a constant altitude of 5100 m a.s.l, and at a mean ground speed of about 280 km h-1. Gravity was measured using a LaCoste & Romberg relative, air/sea gravimeter (type SA) mounted on a laser gyro stabilized platform. Data from 5 GPS antennae located on fuselage and wings and 7 ground-based GPS reference stations were used to determine position and aircraft induced accelerations.The gravimeter passband was derived by comparing the vertical accelerations provided by the gravimeter with those estimated from the GPS positions. This comparison showed that the gravimeter is not sensitive to very short wavelength aircraft accelerations, and therefore a simplified formulation for computing airborne gravity measurements was developed. The intermediate and short wavelength, non-gravitational accelerations were eliminated by means of digital, exponential low-pass filters (cut-off wavelength: 16 km). An important issue in airborne gravimetry is the reliability of the airborne gravity surveys when compared to ground surveys. In our studied area, the differences between the airborne-acquired Bouguer anomaly and the ground upward-continued Bouguer anomaly of the Alps shows a good agreement: the rms of these differences is equal to 7.68 mGal for a spatial resolution of 8 km. However, in some areas with rugged topography, the amplitudes of those differences have a striking correlation with the topography. We then argue that the choice of an appropriate density (reduction by a factor of 10 per cent) for computing the

  8. New gravity maps of the Eastern Alps and significance for the crustal structures

    NASA Astrophysics Data System (ADS)

    Zanolla, Claudio; Braitenberg, Carla; Ebbing, Jörg; Bernabini, Marcello; Bram, Kurt; Gabriel, Gerald; Götze, Hans-Jürgen; Giammetti, Salvatore; Meurers, Bruno; Nicolich, Rinaldo; Palmieri, Franco

    2006-02-01

    The deep seismic profile T RANSALP crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the T RANSALP-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between - 190 * 10 - 5 m/s 2 and + 25 * 10 - 5 m/s 2, with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10 - 5 m/s 2, with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses

  9. Regional lunar gravity anomaly recovery with the GRAIL Level-1b data, and pin-point crustal density estimation with the GRAIL Level-2 and LRO topography data

    NASA Astrophysics Data System (ADS)

    Hashimoto, M.; Heki, K.

    2014-12-01

    We report the lunar gravity anomaly recovery using the GRAIL Level-1b and Level-2 data, downloaded from the PDS Geoscience Node at the Washington University. First, we used the GNV1b (satellite position data) and KBR1b (inter-satellite ranging data) files of the Level-1b data to estimate the surface mass distribution on the Moon following the method of Sugano and Heki (EPS 2004; GRL 2005). We confirmed that we could recover the gravity anomalies similar to the Level-2 data with spatial resolution of ~0.8 degrees using low altitude portions of the data. Next, we downloaded the GRAIL Level-2 data set (spherical harmonics with degree/order complete to 660) together with the topography data by LRO laser altimetry, and tried to estimate the pin-point surface crustal density. First, we selected a certain square as large as ~60 km, and compared the gravity and topography values at grid points within the square. They are roughly proportional, and the slope provides information on the density of the material making the topography. This method, however, causes apparent positive correlation between density and average topographic height of about 0.2 g/cm^3/km. We (wrongly) assume that the mass anomalies lie on the reference surface. Then, the mass above (below) the reference surface is interpreted heavier/lighter than its real density. We performed a-posteriori correction of the altitude-dependent errors in the estimated density. We finally focus on a few positive gravity anomalies on the nearside (such as those close to the Copernicus crater) that are not associated with any topographic high. We will try to constrain the subsurface structure of the dense material responsible for the anomaly using both Level-1b and -2 data.

  10. Gravity is the Key Experiment to Address the Habitability of the Ocean in Jupiter's Moon Europa

    NASA Astrophysics Data System (ADS)

    Sessa, A. M.; Dombard, A. J.

    2013-12-01

    Life requires three constituents: a liquid solvent (i.e., water), a chemical system that can form large molecules to record genetic information (e.g., carbon based) as well as chemical nutrients (e.g., nitrogen, phosphorous), and a chemical disequilibrium system that can provide metabolic energy. While it is believed that there is a saline water layer located between the rock and ice layers in Jupiter's moon Europa, which would satisfy the first requirement, it is unknown if the other conditions are currently met. The likelihood that Europa is a haven for life in our Solar System skyrockets, however, if there is currently active volcanism at the rock-water interface, much the same that volcanic processes enable the chemosynthetic life that forms the basis of deep sea-vent communities at the bottom of Earth's oceans. Exploring the volcanic activity on this interface is challenging, as direct observation via a submersible or high-resolution indirect observations via a dense global seismic network on the surface is at present technically (and fiscally!) untenable. Thus, gravity studies are the best way to explore currently the structure of this all-important interface. Though mostly a silicate body with only a relatively thin (~100 km) layer of water, Europa is different from the terrestrial planets in that this rock-water interface, and not the surface, represents the largest density contrast across the moon's near-surface layers, and thus topography on this interface could conceivably dominate the gravity. Here, we calculate the potential anomalies that arise from topography on the surface, the water-ice interface (at 20 km depth), and the rock-water interface, finding that the latter dominates the free-air gravity at the longest wavelengths (spherical harmonic degrees < 10) and the Bouguer gravity at intermediate wavelengths (degrees ~10-50), and only for the shortest wavelengths (degrees > 50) does the water-ice interface (and presumably mass-density anomalies

  11. MODTOHAFSD — A GUI based JAVA code for gravity analysis of strike limited sedimentary basins by means of growing bodies with exponential density contrast-depth variation: A space domain approach

    NASA Astrophysics Data System (ADS)

    Chakravarthi, V.; Sastry, S. Rajeswara; Ramamma, B.

    2013-07-01

    Based on the principles of modeling and inversion, two interpretation methods are developed in the space domain along with a GUI based JAVA code, MODTOHAFSD, to analyze the gravity anomalies of strike limited sedimentary basins using a prescribed exponential density contrast-depth function. A stack of vertical prisms all having equal widths, but each one possesses its own limited strike length and thickness, describes the structure of a sedimentary basin above the basement complex. The thicknesses of prisms represent the depths to the basement and are the unknown parameters to be estimated from the observed gravity anomalies. Forward modeling is realized in the space domain using a combination of analytical and numerical approaches. The algorithm estimates the initial depths of a sedimentary basin and improves them, iteratively, based on the differences between the observed and modeled gravity anomalies within the specified convergence criteria. The present code, works on Model-View-Controller (MVC) pattern, reads the Bouguer gravity anomalies, constructs/modifies regional gravity background in an interactive approach, estimates residual gravity anomalies and performs automatic modeling or inversion based on user specification for basement topography. Besides generating output in both ASCII and graphical forms, the code displays (i) the changes in the depth structure, (ii) nature of fit between the observed and modeled gravity anomalies, (iii) changes in misfit, and (iv) variation of density contrast with iteration in animated forms. The code is used to analyze both synthetic and real field gravity anomalies. The proposed technique yielded information that is consistent with the assumed parameters in case of synthetic structure and with available drilling depths in case of field example. The advantage of the code is that it can be used to analyze the gravity anomalies of sedimentary basins even when the profile along which the interpretation is intended fails to

  12. Geoid and gravity anomaly data of conjugate regions of Bay of Bengal and Enderby Basin: New constraints on breakup and early spreading history between India and Antarctica

    NASA Astrophysics Data System (ADS)

    Krishna, K. S.; Michael, Laju; Bhattacharyya, R.; Majumdar, T. J.

    2009-03-01

    Timing of breakup of the Indian continent from eastern Gondwanaland and evolution of the lithosphere in the Bay of Bengal still remain as ambiguous issues. Geoid and free-air gravity data of Bay of Bengal and Enderby Basin are integrated with shipborne geophysical data to investigate the early evolution of the eastern Indian Ocean. Geoid and gravity data of the Bay of Bengal reveal five N36°W fracture zones (FZs) and five isolated NE-SW structural rises between the Eastern Continental Margin of India (ECMI) and the 85°E Ridge/86°E FZ. The FZs meet the 86°E FZ at an angle of ˜39°. The rises are associated with low-gravity and geoid anomalies and are oriented nearly orthogonal to the FZs trend. The geoid and gravity data of the western Enderby Basin reveal a major Kerguelen FZ and five N4°E FZs. The FZs discretely converge to the Kerguelen FZ at an angle of ˜37°. We interpret the FZs identified in Bay of Bengal and western Enderby Basin as conjugate FZs that trace the early Cretaceous rifting of south ECMI from Enderby Land. Structural rises between the FZs of Bay of Bengal may either represent fossil ridge segments, possibly have extinct during the early evolution of the Bay of Bengal lithosphere or may have formed later by the volcanic activity accreted the 85°E Ridge. Two different gravity signatures (short-wavelength high-amplitude negative gravity anomaly and relatively broader low-amplitude negative gravity anomaly) are observed on south and north segments of the ECMI, respectively. The location of continent-ocean boundary (COB) is at relatively far distance (100-200 km) from the coastline on north ECMI than that (50-100 km) on the south segment. On the basis of geoid, gravity, and seismic character and orientation of conjugate FZs in Bay of Bengal and western Enderby Basin, we believe that transform motion occurred between south ECMI and Enderby Land at the time of breakup, which might have facilitated the rifting process in the north between

  13. Geodetic and geophysical results from a Taiwan airborne gravity survey: Data reduction and accuracy assessment

    NASA Astrophysics Data System (ADS)

    Hwang, Cheinway; Hsiao, Yu-Shen; Shih, Hsuan-Chang; Yang, Ming; Chen, Kwo-Hwa; Forsberg, Rene; Olesen, Arne V.

    2007-04-01

    An airborne gravity survey was conducted over Taiwan using a LaCoste and Romberg (LCR) System II air-sea gravimeter with gravity and global positioning system (GPS) data sampled at 1 Hz. The aircraft trajectories were determined using a GPS network kinematic adjustment relative to eight GPS tracking stations. Long-wavelength errors in position are reduced when doing numerical differentiations for velocity and acceleration. A procedure for computing resolvable wavelength of error-free airborne gravimetry is derived. The accuracy requirements of position, velocity, and accelerations for a 1-mgal accuracy in gravity anomaly are derived. GPS will fulfill these requirements except for vertical acceleration. An iterative Gaussian filter is used to reduce errors in vertical acceleration. A compromising filter width for noise reduction and gravity detail is 150 s. The airborne gravity anomalies are compared with surface values, and large differences are found over high mountains where the gravity field is rough and surface data density is low. The root mean square (RMS) crossover differences before and after a bias-only adjustment are 4.92 and 2.88 mgal, the latter corresponding to a 2-mgal standard error in gravity anomaly. Repeatability analyses at two survey lines suggest that GPS is the dominating factor affecting the repeatability. Fourier transform and least-squares collocation are used for downward continuation, and the latter produces a better result. Two geoid models are computed, one using airborne and surface gravity data and the other using surface data only, and the former yields a better agreement with the GPS-derived geoidal heights. Bouguer anomalies derived from airborne gravity by a rigorous numerical integration reveal important tectonic features.

  14. Structure and State of Stress of the Chilean Subduction Zone from Terrestrial and Satellite-Derived Gravity and Gravity Gradient Data

    NASA Astrophysics Data System (ADS)

    Gutknecht, B. D.; Götze, H.-J.; Jahr, T.; Jentzsch, G.; Mahatsente, R.; Zeumann, St.

    2014-11-01

    It is well known that the quality of gravity modelling of the Earth's lithosphere is heavily dependent on the limited number of available terrestrial gravity data. More recently, however, interest has grown within the geoscientific community to utilise the homogeneously measured satellite gravity and gravity gradient data for lithospheric scale modelling. Here, we present an interdisciplinary approach to determine the state of stress and rate of deformation in the Central Andean subduction system. We employed gravity data from terrestrial, satellite-based and combined sources using multiple methods to constrain stress, strain and gravitational potential energy (GPE). Well-constrained 3D density models, which were partly optimised using the combined regional gravity model IMOSAGA01C (Hosse et al. in Surv Geophys, 2014, this issue), were used as bases for the computation of stress anomalies on the top of the subducting oceanic Nazca plate and GPE relative to the base of the lithosphere. The geometries and physical parameters of the 3D density models were used for the computation of stresses and uplift rates in the dynamic modelling. The stress distributions, as derived from the static and dynamic modelling, reveal distinct positive anomalies of up to 80 MPa along the coastal Jurassic batholith belt. The anomalies correlate well with major seismicity in the shallow parts of the subduction system. Moreover, the pattern of stress distributions in the Andean convergent zone varies both along the north-south and west-east directions, suggesting that the continental fore-arc is highly segmented. Estimates of GPE show that the high Central Andes might be in a state of horizontal deviatoric tension. Models of gravity gradients from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission were used to compute Bouguer-like gradient anomalies at 8 km above sea level. The analysis suggests that data from GOCE add significant value to the

  15. Deep structure study of the salt body of Jbel Rheouis (central tunisia) from geological and gravity data

    NASA Astrophysics Data System (ADS)

    Bouzid, Wajih; Abbes, Chedly; Gabtni, Hakim; Hassine, Mouna

    2016-04-01

    Jbel Rheouis situated in south west of Sidi Bouzid, central Tunisia, is a complex structure located at a tectonic node between N-S, NE-SW and NW-SE corridors. It was considered as a diapir containing the most complete series of The Upper Triassic formation in Central Tunisia. The good quality of preserved fossils markers especially at the limestone levels made it possible for Burollet (1952) to propose a lithostratigraphic description of the Rheouis Formation. This stratigraphy was clarified by Soussi and Abbes (2004) basing on new paleontological, palynological and outcrops detailed mapping data. Thus, they assigned the base of this outcrops series to Carnian and its top to Rhaetian. Using these geological and lithostratigraphic data we suspects that the base of the Rheouis formation formed by black limestone can be correlated to the Rehach limestone in the South of Tunisia where this level is laying on a clayey sandstones level identified as the Lower Triassic outcrops. In this concept, this study intend to investigate the Rheouis structure and to identify it's nature basing on the intra salt structures identification and the nature of the Lower Triassic sediments buried beneath the Black limestones, using a combination of geological, lithostratigraphic and geophysical (gravity) data. The gravity data used in this work were obtained from the ONM with a mesh of 1Km /1Km. All the data were merged and reduced using the 1967 International gravity formula. Free air and Bouguer gravity correction were made using sea level as a datum and 2.4 g/cm³ as a reduction density. The Bouguer anomaly map shows a variation in anomaly values range from -12.5 mGal to -4.5 mGal with a contrasted anomaly distribution. This map present 5 gravity maxima and 4 gravity minima where the major direction of those maxima and minima are N-S, NE-SW and NW-SE. The presence of a relative positive anomaly concentrated J.Rheouis can be explained by a mass excess probably due to the uplift of the

  16. Gravity anomaly at a Pleistocene lake bed in NW Alaska interpreted by analogy with Greenland's Lake Taserssauq and its floating ice tongue

    USGS Publications Warehouse

    Barnes, D.F.

    1987-01-01

    A possible example of a very deep glacial excavation is provided by a distinctive gravity low located at the front of a valley glacier that once flowed into glacial Lake Aniuk (formerly Lake Noatak) in the western Brooks Range. Geologic and geophysical data suggest that sediments or ice filling a glacially excavated valley are the most probable cause of the 30-50 mGal anomaly. Reasonable choices of geometric models and density contrasts indicate that the former excavation is now filled with a buried-ice thickness of 700 m or sediment thicknesses greater than 1 km. No direct evidence of efficient excavation was observed in Greenland, but efficient glacial erosion behind a floating polar ice tongue could explain the excavation that caused the Alaskan gravity anomaly. -from Author

  17. Determining OCT structure and COB Location of the Omani Gulf of Aden Continental Margin from Gravity Inversion, Residual Depth Anomaly and Subsidence Analysis.

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Leroy, Sylvie; Manatshal, Gianreto

    2013-04-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure and continent-ocean boundary (COB) location, the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust are of critical importance in evaluating rifted continental margin formation and evolution. In order to determine the OCT structure and COB location for the eastern Gulf of Aden, along the Oman margin, we use a combination of gravity inversion, subsidence analysis and residual depth anomaly (RDA) analysis. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted margins. The gravity inversion method, which is carried out in the 3D spectral domain, incorporates a lithosphere thermal gravity anomaly and includes a correction for volcanic addition due to decompression melting. Reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. RDAs have been calculated by comparing observed and age predicted oceanic bathymetries, using the thermal plate model predictions from Crosby and McKenzie (2009). RDAs have been computed along profiles and have been corrected for sediment loading using flexural back-stripping and decompaction. In addition, gravity inversion crustal basement thicknesses together with Airy isostasy have been used to predict a synthetic RDA. The RDA results show a change in RDA signature and may be used to estimate the distal extent of thinned continental crust and where oceanic crust begins. Continental lithosphere thinning has been determined using flexural back-stripping and subsidence analysis assuming the classical rift model of McKenzie (1978) with a correction for

  18. Compositional Density Structure of the Upper Mantle from Constrained 3-D Inversion of Gravity Anomaly: A Case Study of Southeast Asia

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Chen, C.; Kaban, M. K.; Thomas, M.

    2014-12-01

    Mantle density structure is a key for tectonics. The density variations in the upper mantle are affected by temperature and composition. Seismic tomography method has been widely applied to obtain the P- and S-wave velocity structure in the mantle, which is then used to calculate the density perturbation. However, the velocity model is mainly due to the thermal effects but not the compositional effects. A method of 3-D inversion of gravity anomaly developed in spherical coordinates is used to image the large-scale density structure of upper mantle in Southeast Asia. The mantle gravity anomalies used in inversion are calculated by removing the crustal effects from the observed gravity. With constraints of thermal density model from seismic tomography, the integrative density structure is estimated from gravity inversion. Consequently, we obtain the compositional density by subtracting the thermal density from the integrative structure. The result of inversion shows the anisotropic composition of subduction zones, Cratons and plates boundary in Southeast Asia. In the shallow depth, the compositional density anomalies of large scales present uniform features in oceanic and continental mantle. In depth of 75-175 km, there are differences between the thermal and the compositional variations. The density anomalies at these depths are both affected by temperature and composition of the upper mantle. Below 175-km depth, the density anomalies are dominated by the compositional variations. Furthermore, comparing with high seismicity occurred at moderate-depth (50-300 km), we found that the compositional density variations is one of the factor that inducing earthquakes. The constrained inversion of mantle gravity anomaly has possibility to reveal the subduction which is not clearly seen from low-resolution tomography data, and may reveal the relation of seismicity and composition in the upper mantle. This study is supported by the Program of International Science and

  19. World Gravity Map (WGM) Project: Objectives and Status

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Briais, A.; Peyrefitte, A.; Biancale, R.; Gabalda, G.; Moreaux, G.; Sarrailh, M.; Fayard, T.

    2009-12-01

    The WGM project is a gravity mapping project undertaken under the aegis of the Commission for the Geological Map of the World (CGMW) to complement a set of global geological and geophysical digital maps published and updated by CGMW, such as the World Digital Magnetic Anomaly Map (WDMAM), released in 2007. This new global digital map aims to provide a high-resolution picture of the gravity anomalies of the world (free-air and topography-corrected Bouguer) based on the available information on the Earth gravity field, with the final objective to contribute to research and educational projects. The WGM project is conducted by the International Gravimetric Bureau (IGB), a center of the International Gravity Field Service (IGFS) of the International Association of Geodesy (IAG), with the support of the United Nations Educational Scientific and Cultural Organization (UNESCO). Major contributions to the WGM are provided by the EGM08 global model, recently released by the National Geospatial-Intelligence Agency (NGA, USA), as well as the new global marine gravity fields derived from satellite altimetry (DNSC08 computed at the Danish National Space Center, and V18.1 computed at Scripps Institution of Oceanography). The WGM also aims to improve the gravity anomalies at regional scale, using available products from recent regional compilations of land, marine and airborne surveys (possibly derived from BGI or other global or regional databases). As other geophysical maps published by CGMW, the WGM maps and digital products should be regularly updated according to the incoming gravity datasets. We present here the current status of the WGM project.

  20. Study of satellite geoid and gravity anomaly data of conjugate regions of Bay of Bengal and Enderby Basin new constraints on early evolution of the eastern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Krishna, K. S.; Michael, L.; Bhattacharyya, R.; Majumdar, T. J.; Chatterjee, S.

    2006-12-01

    Timing for breakup of the Indian plate from eastern Gondwanaland and evolution of the lithosphere in the Bay of Bengal still remain debated because of lack of confident identification of seafloor spreading magnetic anomalies and fracture zones. Satellite geoid and gravity data of the two conjugate regions, Bay of Bengal (BOB) and Enderby Basin (EB), are coupled with ship-borne data for investigation of early evolution of the eastern Indian Ocean, particularly the lithosphere formed earlier to seafloor magnetic anomaly 34. The magnetic anomaly 34 is identified with greater confidence in north and northwestern periphery of the EB and in the distal Bengal Fan region. In BOB no correlatable magnetic anomaly related to M-sequence is identified, therefore EB holds the key for understanding of the breakups that had occurred between eastern margin of India and east Antarctica. Recent identifications of pairs of M-sequence anomalies (from M9N to M2) and extinct ridge segment in the eastern Enderby Basin suggest that formation of the lithosphere in the BOB was no earlier than anomaly M2. High-resolution geoid and gravity data of the BOB reveal the presence of prominent tectonic features such as Sunda trench, Ninetyeast and 85°E ridges, etc. Geoidal gradient of the BOB trends in WSW-ENE direction and does not follow the direction of the plate motion as expected, instead it trends in the resultant direction between the plate motion direction and geoidal low lying south of Sri Lanka. While in the EB the geoidal gradients trend in N-S to NW-SE following the general trends of the plate motion directions. Two prominent NW-SE trending fracture zones and five isolated NE-SW elongated structural rises are observed in residual geoidal and free-air gravity anomaly data between eastern margin of India and the 85°E Ridge. The rises are associated with low gravity anomalies and are oriented in orthogonal to the fracture zones trend. We interpret these structures as extinct ridge

  1. Gravity field over the Sea of Galilee: Evidence for a composite basin along a transform fault

    USGS Publications Warehouse

    Ben-Avraham, Z.; ten Brink, U.; Bell, R.; Reznikov, M.

    1996-01-01

    The Sea of Galilee (Lake Kinneret) is located at the northern portion of the Kinneret-Bet Shean basin, in the northern Dead Sea transform. Three hundred kilometers of continuous marine gravity data were collected in the lake and integrated with land gravity data to a distance of more than 20 km around the lake. Analyses of the gravity data resulted in a free-air anomaly map, a variable density Bouguer anomaly map, and a horizontal first derivative map of the Bouguer anomaly. These maps, together with gravity models of profiles across the lake and the area south of it, were used to infer the geometry of the basins in this region and the main faults of the transform system. The Sea of Galilee can be divided into two units. The southern half is a pull-apart that extends to the Kinarot Valley, south of the lake, whereas the northern half was formed by rotational opening and transverse normal faults. The deepest part of the basinal area is located well south of the deepest bathymetric depression. This implies that the northeastern part of the lake, where the bathymetry is the deepest, is a young feature that is actively subsiding now. The pull-apart basin is almost symmetrical in the southern part of the lake and in the Kinarot Valley south of the lake. This suggests that the basin here is bounded by strike-slip faults on both sides. The eastern boundary fault extends to the northern part of the lake, while the western fault does not cross the northern part. The main factor controlling the structural complexity of this area is the interaction of the Dead Sea transform with a subperpendicular fault system and rotated blocks.

  2. Large-scale gravity anomaly in northern Norway: tectonic implications of shallow or deep source depth and a possible conjugate in northeast Greenland

    NASA Astrophysics Data System (ADS)

    Gradmann, Sofie; Ebbing, Jörg

    2015-12-01

    A prominent gravity and geoid low lies just south of the Lofoten peninsula in northern Norway, partly coinciding with the location of Proterozoic granites of the Transscandinavian Igneous Belt and being offset by ca. 100 km to the highest topography of northern Norway. The study area extends both onshore and offshore and lies at the transition between Archaean and Proterozoic lithosphere. The Palaeoproterozoic basement has been overthrusted by the Palaeozoic nappes of the Caledonian orogen and now forms the passive margin of the NE Atlantic. We investigate the gravity anomaly performing combined 3-D geophysical-petrological forward modelling of the lithosphere and sublithospheric upper mantle using the interactive modelling program LitMod3D. We include variations in thickness and composition of the lithospheric mantle in order to include the effects on the rifted margin adjoining the Baltic craton. We compare three possible origins of the anomaly: (i) a low-density upper crust, representing the northward extension of the Transscandinavian Igneous Belt, (ii) a lower crustal source formed by a Moho depression and (iii) a thick, depleted lithospheric mantle of possibly Archaean origin. A similar, yet wider and stronger gravity anomaly is found on the conjugate margin in northeastern Greenland. A shallow crustal source is most consistent with the geophysical data sets. A respective source of the granitic belt, however, is difficult to reconcile with the regional geology both in Fennoscandia and Greenland. An additional contribution form a deeper source is suggested.

  3. 3DINVER.M: a MATLAB program to invert the gravity anomaly over a 3D horizontal density interface by Parker Oldenburg's algorithm

    NASA Astrophysics Data System (ADS)

    Gómez-Ortiz, David; Agarwal, Bhrigu N. P.

    2005-05-01

    A MATLAB source code 3DINVER.M is described to compute 3D geometry of a horizontal density interface from gridded gravity anomaly by Parker-Oldenburg iterative method. This procedure is based on a relationship between the Fourier transform of the gravity anomaly and the sum of the Fourier transform of the interface topography. Given the mean depth of the density interface and the density contrast between the two media, the three-dimensional geometry of the interface is iteratively calculated. The iterative process is terminated when either the RMS error between two successive approximations is lower than a pre-assigned value—used as convergence criterion, or until a pre-assigned maximum number of iterations is reached. A high-cut filter in the frequency domain has been incorporated to enhance the convergence in the iterative process. The algorithm is capable of handling large data sets requiring direct and inverse Fourier transforms effectively. The inversion of a gravity anomaly over Brittany (France) is presented to compute the Moho depth as a practical example.

  4. Structural interpretation of the Erzurum Basin, eastern Turkey, using curvature gravity gradient tensor and gravity inversion of basement relief

    NASA Astrophysics Data System (ADS)

    Oruç, B.; Sertçelik, İ.; Kafadar, Ö.; Selim, H. H.

    2013-01-01

    The Erzurum Basin has received more attention in petroleum potential research because of its particularity in geographic and tectonic position. There remains debate on the basement structure of the basin since igneous rocks and faults make the structure and stratigraphy more complicated. We utilize gravity data to understand the structure of the Erzurum Basin. This study describes an edge enhancement technique based on the eigenvalues and determinant obtained from the curvature gravity gradient tensor (CGGT). The main goal of this technique is to delineate structural boundaries in complex geology and tectonic environment using CGGT. The results obtained from theoretical data, with and without Gaussian random noise, have been analyzed in determining the locations of the edges of the vertical-sided prism models. The zero contours of the smallest eigenvalue delineate the spatial location of the edges of the anomalous sources. In addition, 3-D gravity inversion of Bouguer anomalies has been used with purpose to estimate the structure of the substrata to allow modeling of the basement undulation in the Erzurum basin. For this reason, the Parker-Oldenburg algorithm helped to investigate this undulation and to evidence the main linear features. This algorithm reveals presence of basement depths between 3.45 and 9.06 km in the region bounded by NE-SW and E-W trending lineaments. We have also compared the smallest eigenvalue zero contours with the HGM images and Tilt derivative (TDR) of Bouguer anomaly map of the study area. All techniques have agreed closely in detecting the horizontal locations of geological features in the subsurface with good precision.

  5. OCT structure, COB location and magmatic type of the S Angolan & SE Brazilian margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Horn, Brian

    2014-05-01

    Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been applied to the S Angolan and SE Brazilian margins to determine OCT structure, COB location and magmatic type. Knowledge of these margin parameters are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the S Angolan and SE Brazilian rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated for profiles Lusigal 12 and ISE-01 on the Iberian margin. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola deep seismic reflection lines. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along the seismic profiles. Gravity inversion, RDA and subsidence analysis along the ION-GXT BS1-575 profile, which crosses the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin, predict the COB to be located SE of the Florianopolis Ridge. Integrated quantitative analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts oceanic crustal thicknesses of between 7 and 8 km thickness with

  6. Imaging the Buried Chicxulub Crater with Gravity Gradients and Cenotes

    NASA Astrophysics Data System (ADS)

    Hildebrand, A. R.; Pilkington, M.; Halpenny, J. F.; Ortiz-Aleman, C.; Chavez, R. E.; Urrutia-Fucugauchi, J.; Connors, M.; Graniel-Castro, E.; Camara-Zi, A.; Vasquez, J.

    1995-09-01

    Differing interpretations of the Bouguer gravity anomaly over the Chicxulub crater, Yucatan Peninsula, Mexico, have yielded diameter estimates of 170 to 320 km. Knowing the crater's size is necessary to quantify the lethal perturbations to the Cretaceous environment associated with its formation. The crater's size (and internal structure) is revealed by the horizontal gradient of the Bouguer gravity anomaly over the structure, and by mapping the karst features of the Yucatan region. To improve our resolution of the crater's gravity signature we collected additional gravity measurements primarily along radial profiles, but also to fill in previously unsurveyed areas. Horizontal gradient analysis of Bouguer gravity data objectively highlights the lateral density contrasts of the impact lithologies and suppresses regional anomalies which may obscure the gravity signature of the Chicxulub crater lithologies. This gradient technique yields a striking circular structure with at least 6 concentric gradient features between 25 and 85 km radius. These features are most distinct in the southwest probably because of denser sampling of the gravity field. Our detailed profiles detected an additional feature and steeper gradients (up to 5 mGal/km) than the original survey. We interpret the outer four gradient maxima to represent concentric faults in the crater's zone of slumping as is also revealed by seismic reflection data. The inner two probably represent the margin of the central uplift and the peak ring and or collapsed transient cavity. Radial gradients in the SW quadrant over the inferred ~40 km-diameter central uplift (4) may represent structural "puckering" as revealed at eroded terrestrial craters. Gradient features related to regional gravity highs and lows are visible outside the crater, but no concentric gradient features are apparent at distances > 90 km radius. The marginal gradient features may be modelled by slump faults as observed in large complex craters on

  7. Assessment Ground Safety Using Time Lap Vertical Gravity Gradient At The Subsidence Area

    NASA Astrophysics Data System (ADS)

    Rim, H. B.; Park, Y.; Lim, M.; Koo, S. B.; Kwon, B. D.

    2007-05-01

    We have carried out time-lap vertical gravity gradient (VGG) survey in order to assess the ground safety before and after grouting. The target area is new pavement through the rice field, and the area has subsidence problems because of excessive pumping for agricultural irrigation. Therefore, it has been reinforced with cement grouting avoiding subsidence. In this paper, we examined the change of subsurface density distribution due to cement grouting by means of VGG survey. VGG method is more sensitive to detect the change of near surface than gravity survey itself because VGG enhanced small variation of gravity anomaly. We gathered one line gravity data about 270m long at every 2m. VGG survey consisted of observations between the ground bottom and the top separated vertically about 1.5m with help of the ladder specially designed. According to result, VGG anomaly made the response of man-made waterway clearer than Bouguer anomaly in the middle part of the line. And VGG result showed changes of subsurface density distribution after grouting.

  8. Gravity

    NASA Astrophysics Data System (ADS)

    Poisson, Eric; Will, Clifford M.

    2014-05-01

    Preface; 1. Foundations of Newtonian gravity; 2. Structure of self-gravitating bodies; 3. Newtonian orbital dynamics; 4. Minkowski spacetime; 5. Curved spacetime; 6. Post-Minkowskian theory: formulation; 7. Post-Minkowskian theory: implementation; 8. Post-Newtonian theory: fundamentals; 9. Post-Newtonian theory: system of isolated bodies; 10. Post-Newtonian celestial mechanics, astrometry and navigation; 11. Gravitational waves; 12. Radiative losses and radiation reaction; 13. Alternative theories of gravity; References; Index.

  9. The structural setting of the Ischia Island Caldera (Italy): first evidence from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Capuano, Paolo; De Matteis, Raffaella; Russo, Guido

    2015-09-01

    Ischia Island is one of the active volcanoes of the Neapolitan area (Italy). Hazard assessment of active, densely populated volcano is primarily based on knowledge of the volcano's past behaviour and of its present state. As a contribution to the definition of the present structural setting of Ischia Island, we constructed a new model of the shallow crust using geophysical data: seismic wave travel times and Bouguer anomaly data. We analysed these data sets through seismic tomography and gravity data inversion. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rim along the perimeter of the island, as hypothesized by many authors, and the presence of a high velocity and density area inside the caldera consistent with extension of the resurgent block that characterizes the recent deformation of the island.

  10. The Emerson Lake Body: A link between the Landers and Hector Mine earthquakes, southern California, as inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.

    2002-01-01

    Gravity and magnetic data indicate a mafic crustal heterogeneity that lies between the Hector Mine 16 October 1999 (Mw 7.1) and Landers 28 June 1992 (Mw 7.3) epicenters. The aftershocks and ruptures of these two events avoided the interior of the body. Two- and three-dimensional modeling of the potential-field anomalies shows that the source, here named the Emerson Lake body (ELB), extends to a depth of approximately 15 km. The source of the gravity and magnetic anomaly is most likely Jurassic diorite because exposures of these rocks coincide with both gravity and magnetic highs west of Emerson Lake. Seismic tomography also shows higher velocities within the region of the ELB. We propose that the ELB was an important influence on the rupture geometry of the Landers and Hector Mine ruptures and that the ELB may have played a role in transferring of stress from the Landers earthquake to the Hector Mine hypocenter. Seismicity before the Landers earthquake also tended to avoid the ELB, suggesting that the ELB affects how strain is distributed in this part of the Mojave Desert. Thus, faults within the body should have limited rupture sizes and lower seismic hazard than faults bounding or outside this mafic crustal heterogeneity.

  11. Detection of High-Potential Oil and Gas Fields Using Normalized Full Gradient of Gravity Anomalies: A Case Study in the Tabas Basin, Eastern Iran

    NASA Astrophysics Data System (ADS)

    Aghajani, Hamid; Moradzadeh, Ali; Zeng, Hualin

    2011-10-01

    The normalized full gradient (NFG) represents the full gradient of the gravity anomaly at a point divided by the average of the full gradient at the same point. The NFG minimum between two maxima in an NFG section or a closed minimum surrounded by closed maxima on an NFG map may indicate density-deficient anomalies closely related to possible oil-gas reservoirs. On a cross-section, closed minima can be used to estimate the depth to centers of possible hydrocarbon reservoirs. The NFG map can also be used to locate oil-gas exploratory wells for estimation of the depth of possible reservoirs. The objective of this paper is to use two and three-dimensional (2D and 3D) NFG on gravity data of the Tabas basin in Yazd province, eastern Iran. A hypothetical model is first considered to explore the NFG characteristics and their relationship with the geometry of the model. The physical properties of the model are then studied to simplify the interpretation of real data. Finally 2D and 3D NFG models are developed for real gravity data to predict the location of any possible high potential oil-gas reservoirs. The results obtained indicate two zones in the northern and central parts of the Tabas basin suitable for hydrocarbon prospecting. However, the favorable zone located in the middle of the basin in which anticline E is detected at a depth of 5-7 km is more important for the purpose of hydrocarbon exploration.

  12. Analysis of gravity data in Central Valleys, Oaxaca, southern, Mexico

    NASA Astrophysics Data System (ADS)

    Gonzalez, T.; Ferrusquia, I.

    2015-12-01

    The region known as Central Valleys is located in the state of Oaxaca, southern, Mexico (16.3o- 17.7 o N Lat. and 96 o - 97 o W Long.) In its central portion is settled the capital of the state. There are very few published detailed geological studies.. Geomorphological and geological features, indicates that Central Valleys and surrounding mountains conform a graben structure. Its shape is an inverted Y, centred on Oaxaca City. The study area was covered by a detailed gravity survey with a homogenous distribution of stations. The Bouguer gravity map is dominated by a large gravity low, oriented NW-SE. In order to know the characteristics of anomalies observed gravity, data transformations were used. The use of spectral methods has increased in recent years, especially for the estimation of the depth of the source. Analysis of the gravity data sheds light on the regional depth of the Graben basement and the spatial distribution of the volcanic rocks

  13. OCT structure, COB location and magmatic type of the SE Brazilian & S Angolan margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data

    NASA Astrophysics Data System (ADS)

    Cowie, L.; Kusznir, N. J.; Horn, B.

    2013-12-01

    Knowledge of ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and magmatic type are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the SE Brazilian and S Angolan rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been used to determine OCT structure, COB location and magmatic type for the SE Brazilian and S Angolan margins. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated on the Iberian margin for profiles IAM9 and ISE-01. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along profile. Gravity inversion, RDA and subsidence analysis along the S Angolan ION-GXT CS1-2400 profile has been used to determine OCT structure and COB location. Analysis suggests that exhumed mantle, corresponding to a magma poor margin, is absent beneath the allochthonous salt. The thickness of earliest oceanic crust, derived from gravity and deep seismic reflection data is approximately 7km. The joint inversion predicts crustal basement densities and seismic velocities which are

  14. Geomodel constructs of the Earth's crust for water continuation of the Korotaikha depression from gravity and magnetic data for revealing promising areas of oil and gas accumulation

    NASA Astrophysics Data System (ADS)

    Litvinova, Tamara; Kudryavtsev, Ivan

    2016-04-01

    The paper considers the results of re-interpretation of geophysical data within the water continuation of the Korotaikha depression. To solve the issue of identifying promising areas of oil and gas accumulation in the region, magnetic and gravity materials were reprocessed: digital maps of potential fields at 1: 500 000 scale were compiled on a frame network of seismic lines (3 lines on land and 3 lines in water area) made by reflection-CDP, density models to a depth of 20 km by solving the direct problem of gravity prospecting in GM-SYS module (Geosoft) in 2D formulation were constructed. Deep reflection-CDP seismic sections specified according to the deep wells were used as starting models. Correctness of the selected density models was controlled by comparing the theoretical curve with the values interpolated on the profile line from the digital model of gravity anomaly (Bouguer, density of the intermediate layer of 2.67 g/cm3). Magnetic modeling was performed using geometry of blocks from the obtained density models to a depth of 20 km and is based on selection of local anomaly sources in the upper section (in the Triassic strata). Blocks of the Precambrian basement were used as sources of regional magnetic anomalies in the considered models. Modeling constructs show the defining role of the topography of terrigenous and carbonate complex boundary within the Paleozoic section as a source of gravity anomalies for the region under study. These findings are confirmed by comparison of gravity and seismic data (maps of local gravity anomalies and structural maps of reflecting horizons) and additionally substantiated by analysis of the nature of local magnetic anomalies distribution. The latter are associated with the Triassic basalt horizons at the top of the terrigenous complex and thus also reflect structures of the sedimentary cover, which are registered independently by gravity data.

  15. Gravity anomalies, Quaternary vents, and Quaternary faults in the southern Cascade Range, Oregon and California: Implications for arc and backarc evolution

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Christiansen, Robert L.; Guffanti, Marianne; Wells, Ray E.; Donnelly-Nolan, Julie M.; Muffler, L. J. Patrick; Clynne, Michael A.; Smith, James G.

    1997-10-01

    Isostatic residual gravity anomalies in the southern Cascade Range of northern California and southern Oregon are spatially correlated with broad zones of Quaternary magmatism as reflected by the total volume of Quaternary volcanic products, the distribution of Quaternary vents, and the anomalously low teleseismic P wave velocities in the upper 30 km of crust. The orientation of Quaternary faults also appears to be related to gravity anomalies and volcanism in this area, trending generally north-south within the magmatic regions and northwest-southeast as they enter the neighboring amagmatic zones to the north and south. The relationship between gravity anomalies, vent density, and fault orientations may indicate in a broad sense the strength of the middle and upper crust. The southern Cascade Range occupies a transition zone where horizontal stress is transferred from the northwest-southeast dextral shear of the Walker Lane belt to the east-west extension characteristic of the Cascade arc in central Oregon. Faulting along north-south strikes in the volcanically active areas indicates the east-west extensional stresses in thermally weakened crust, whereas northwest faulting between the volcanically active areas reflects the northwest trending, right lateral shear strain of the Walker Lane belt. The segmentation of the arc reflected in Quaternary magmatism may be caused by differential extension behind crustal blocks of the forearc rotating clockwise with respect to North America. In this view the volcanic centers at Mount Shasta, Medicine Lake volcano, and Lassen Peak in northern California are situated along the southern parts of the trailing edges of two distinct segments of the forearc where additional extension is implied by their differential clockwise rotation.

  16. 3D inversion of lunar gravity data and preliminary results

    NASA Astrophysics Data System (ADS)

    Liang, Q.; Chen, C.; Li, Y.

    2010-12-01

    Gravity anomaly tells how the subsurface density varies or where the mass concentrations are located at. Inversion of gravity data gives a way to directly recover the density distributions. It has been demonstrated that the inversion is capable of retrieving density structures in resources exploration on the Earth. With increasing interests in interior structures of the Moon, scientists have obtained its gravity field with improved resolution on the lunar far side. We may thus utilize the inverse method to recover the lunar density structures beneath mascon basins or the density inhomogeneities in the crust and mantle. However, if considering the spherical gravity data in global scale, there are limitations in the previous inversion because the methods were based on the Cartesian coordinates system. In order to solve the problems, we developed a new 3D inverse method with three aspects involved: 1) A new model objective function adaptive to spherical coordinate system was established in the light of the Backus-Gilbert model appraisal theory. 2) A depth weighting function in inversion was also developed to approximately compensate for the kernel’s natural decay in potential field. And, 3) Non-uniqueness was suppressed by using model constraints and Tikhonov regularization tool. With the above developments and techniques, our method can quantitatively interpret the spherical gravity data. We firstly performed the inversion of synthetic data and confirmed that the locations of anomaly bodies were well defined, and then applied this method to the Bouguer gravity anomaly of the Moon which has been previously calculated based on the Chang'E-1 topography data and the SELENE gravity field model. Results showed that, on the one hand, the positive density anomalies beneath the mascon basins concentrated at the depth of 20-50km. Their residual densities are larger than 0.3g/cm^3 close to the density difference between lunar mantle and crust. Density structures along radial

  17. Airborne Gravity Measurements using a Helicopter with Special Emphases on Delineating Local Gravity Anomalies Mainly for Detecting Active Seismic Faults (Invited)

    NASA Astrophysics Data System (ADS)

    Segawa, J.

    2010-12-01

    The first aerial gravity measurement in Japan started in 1998 using a Japanese airborne gravimeter ‘ Segawa-TKeiki airborne gravimeter Model FGA-1’. We lay emphasis on the measurement of detailed gravity structures at the land-to-sea border areas and mountainous areas. This is the reason why we use a helicopter and make surveys at low altitude and low speed. We have so far made measurement at twelve sites and the total flight amounts to 20,000km. The accuracy of measurement is 1.5 mgal and half-wavelength resolution is 1.5 km. The Japanese type gravimeter consists of a servo-accelerometer type gravity sensor, a horizontal platform controlled by an optical fiber gyro, GPS positioning system, and a data processing system. Helicopter movement has to be precisely monitored three-dimensionally to calculate the vehicle’s acceleration noises. The necessary accuracy of positioning of the vehicle must be better than 10 cm in positioning error. Our helicopter gravity measurement has a special target in Japan to investigate active seismic faults located across land-to-sea borderlines. In Japan, it is generally thought that gravity over most of the country has already been measured by the governmental surveys, leaving the land-sea border lines and mountainous zones unsurveyed as difficult-to-access areas. In addition the use of airplane or helicopter in Japan appeared disadvantageous because of the narrowness of the Japanese Islands. Under such situations the author thought there still remained a particular as well as unique need for aerial gravity measurement in Japan, i.e. the need for detailed and seamless knowledge of gravity structures across land-to-sea border lines to elucidate complicated crustal structures of the Japanese Islands as well as distribution of active seismic faults for disaster prevention. The results of gravity measurements we have conducted so far include those of 12 sites. In the following the brief logs of our measurements are listed. 1)April

  18. Shallow structure beneath the Central Volcanic Complex of Tenerife from new gravity data: Implications for its evolution and recent reactivation

    NASA Astrophysics Data System (ADS)

    Gottsmann, J.; Camacho, A. G.; Martí, J.; Wooller, L.; Fernández, J.; García, A.; Rymer, H.

    2008-07-01

    We present a new local Bouguer anomaly map of the Central Volcanic Complex (CVC) of Tenerife, Spain, constructed from the amalgamation of 323 new high precision gravity measurements with existing gravity data from 361 observations. The new anomaly map images the high-density core of the CVC and the pronounced gravity low centred in the Las Cañadas caldera in greater detail than previously available. Mathematical construction of a sub-surface model from the local anomaly data, employing a 3D inversion based on "growing" the sub-surface density distribution via the aggregation of cells, enables mapping of the shallow structure beneath the complex, giving unprecedented insights into the sub-surface architecture. We find the resultant density distribution in agreement with geological and other geophysical data. The modelled sub-surface structure supports a vertical collapse origin of the caldera, and maps the headwall of the ca. 180 ka Icod landslide, which appears to lie buried beneath the Pico Viejo-Pico Teide stratovolcanic complex. The results allow us to put into context the recorded ground deformation and gravity changes at the CVC during its reactivation in spring 2004 in relation to its dominant structural building blocks. For example, the areas undergoing the most significant changes at depth in recent years are underlain by low-density material and are aligned along long-standing structural entities, which have shaped this volcanic ocean island over the past few million years.

  19. Structure and segmentation of the eastern Gulf of Aden basin and the Sheba ridge from gravity, bathymetric and magnetic anomalies: implications for accretion processes

    NASA Astrophysics Data System (ADS)

    D'Acremont, E.; Leroy, S.; Maia, M.; Gente, P.; Autin, J.

    2007-12-01

    The eastern Gulf of Aden is a key place for investigating seafloor spreading processes and the evolution in space and time of the margin and ridge segmentation. The rifting of the Gulf that separated Arabia from Somalia started around 35 Ma ago followed by oceanic accretion from at least17.6 Ma. Bathymetric, gravity and magnetic data from the Encens-Sheba cruise are used to study the structure and segmentation of the eastern part of the basin and ridge, which have strong implications for accretion processes. The segmentation of the first oceanic spreading centre, which is dated at least 17.6 Ma by the magnetic anomaly (A5d) identification, seems to be directly related to the structural geometry of the margins. Then, magmatic processes governed the evolution of the segmentation. The segmentation of the oceanic crust evolved, by eastward propagation of the western segment, from three segments (from an5d to an5) to two segments (from an5). At 6 Ma (an3a) a third segment appeared by duplication of the Socotra transform fault, maybe due to a regional kinematics change. The Encens-Sheba oceanic domain is divided in two distinct areas trending NE-SW perpendicular to the Sheba ridge. (1) The Eastern area is characterized by a shorter wavelength variation of the axial segmentation with two spreading segments 30 to 40 km long, and by a thin crust particularly on the northern and southern ends of its flanks. (2) The Western zone, whose axial segment is more than 120 km long, is characterized by a thick crust and/or a hot mantle and no axial rift valley. This abnormal volcanic activity for a slow spreading ridge is emphasized by bathymetric highs with 5-10 km wide volcanic edifices, and by a negative anomaly of the MBA. These different results support the presence of an off-axis thermal anomaly located below the southern flank of the Sheba ridge. The magnetic anomalies and spreading asymmetry reveal that the location of this thermal anomaly might be relatively recent (~ 10 Ma

  20. Interpretation of gravity and geoid in the Central Andes between 20 ° and 29 ° S

    NASA Astrophysics Data System (ADS)

    Götze, Hans-Jürgen; Kirchner, Andreas

    1997-03-01

    Most recently the MIGRA group with participants from Chile, Argentina and Germany has surveyed some 3.500 new gravity observations in an Andean Geotraverse covering N-Chile and NW-Argentina between 64 °-71 °W and 20 °-29 °S. MIGRA is an international gravity research group which was established under the umbrella of the "Collaborative Research Center" "Deformation Processes in the Andes" at Freie Universität Berlin (Germany). Oil and mining industry gravity data were reprocessed and included into the MIGRA data base which contains more than 15.000 gravity data at present. Due to big logistical problems (terrain access, no maps, no levelling lines etc.) the overall error of the calculated gravity anomalies results of approximately 4-5 mGal which is about 1% compared with the magnitude of about 450 mGal of the Bouguer anomaly. Under the framework of the interdisciplinary research project CINCA (Crustal Investigations Off- and Onshore Nazca/Central Andes) gravity surveys of the MIGRA group has been extended to the Pacific ocean. In summer 1995 MIGRA took part in the "CINCA" offshore experiment SO-104 of the German Research Vessel "Sonne" between the latitudes 20 °S and 24 °S. The data base which includes point data and 10 km ∗ 10 km data grids of free-air-, different types of Bouguer- and isostatic-residual anomalies are presented here in maps of the isostatic residual field along with an interpretation by 3D density modelling. Constraints were mainly taken from results of 2D ray tracing refraction seismics and tectonics. Offset-free modelling is achieved by fitting both gravity field and geoid with one density structure of the lithosphere-system and by modelling relative to a reference density structure derived from the Preliminary Referende Earth Model (PREM, Dziewonski and Anderson, 1981). mGal is used throughout this paper: 1 mGal = 10 -5 m s -1.

  1. GMinterp, A Matlab Based Toolkit for Gravity and Magnetic Data Analysis: Example Application to the Airborne Magnetic Anomalies of Biga Peninsula, NW Turkey

    NASA Astrophysics Data System (ADS)

    Ekinci, Y. L.; Yiǧitbaş, E.

    2012-04-01

    The analysis of gravity and magnetic field methods is becoming increasingly significant for the earth sciences as a whole and these potential field methods efficiently assist in working out both shallow and deep geologic problems and play important role on modeling and interpretation procedures. The main advantage of some gravity and magnetic data processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. If the data quality permits, many analyzing techniques can be carried out that help to build a general understanding of the details and parameters of the shallower or deeper causative body distributions such as depth, thickness, lateral and vertical extensions. Gravity and magnetic field data are usually analyzed by means of analytic signal (via directional derivatives) methods, linear transformations, regional and residual anomaly separation techniques, spectral methods, filtering and forward and inverse modeling techniques. Some commercial software packages are commonly used for analyzing potential field data by employing some of the techniques specified above. Additionally, many freeware and open-source codes can be found in the literature, but unfortunately they are focused on special issues of the potential fields. In this study, a toolkit, that performs numerous interpretation and modeling techniques for potential field data, is presented. The toolkit, named GMinterp, is MATLAB-based consisting of a series of linked functions along with a graphical user interface (GUI). GMinterp allows performing complex processing such as transformations and filtering, editing, gridding, mapping, digitizing, extracting cross-sections, forward and inverse modeling and interpretation tasks. The toolkit enables to work with both profile and gridded data as an input file. Tests on the theoretically produced data showed the reliability of

  2. Structure of the Presidio Bolson area, Texas, interpreted from gravity data

    SciTech Connect

    Mraz, J.R.; Keller, G.R.

    1980-01-01

    To obtain a better understanding of the structure and tectonism of the region, an integrated geophysical-geological study of the Presidio area, Texas, was undertaken using gravity measurements and deep drilling data. New gravity data were combined with existing data to construct simple Bouguer anomaly maps of the Presidio area, and two-dimensional computer modeling of gravity profiles was used to derive earth models. These data outline the major geologic features of the area that are dominated by the effects of Tertiary block faulting and volcanism. The main feature of interest was the Presidio Graben, which is approximately 1.5 km deep near Ruidosa, Texas. One motivation for this study was the collection of a part of the basic scientific data needed to assess the geothermal potential of the area, and the results obtained support the hypothesis that hot springs associated with the Presidio Graben derive their heat from deep circulation along its boundary faults. However, some gravity anomalies observed could be interpreted as indicating the presence of late Tertiary intrusions that could provide heat for the hot springs.

  3. High-resolution gravity and geoid models in Tahiti obtained from new airborne and land gravity observations: data fusion by spectral combination

    NASA Astrophysics Data System (ADS)

    Shih, Hsuan-Chang; Hwang, Cheinway; Barriot, Jean-Pierre; Mouyen, Maxime; Corréia, Pascal; Lequeux, Didier; Sichoix, Lydie

    2015-08-01

    For the first time, we carry out an airborne gravity survey and we collect new land gravity data over the islands of Tahiti and Moorea in French Polynesia located in the South Pacific Ocean. The new land gravity data are registered with GPS-derived coordinates, network-adjusted and outlier-edited, resulting in a mean standard error of 17 μGal. A crossover analysis of the airborne gravity data indicates a mean gravity accuracy of 1.7 mGal. New marine gravity around the two islands is derived from Geosat/GM, ERS-1/GM, Jason-1/GM, and Cryosat-2 altimeter data. A new 1-s digital topography model is constructed and is used to compute the topographic gravitational effects. To use EGM08 over Tahiti and Moorea, the optimal degree of spherical harmonic expansion is 1500. The fusion of the gravity datasets is made by the band-limited least-squares collocation, which best integrates datasets of different accuracies and spatial resolutions. The new high-resolution gravity and geoid grids are constructed on a 9-s grid. Assessments of the grids by measurements of ground gravity and geometric geoidal height result in RMS differences of 0.9 mGal and 0.4 cm, respectively. The geoid model allows 1-cm orthometric height determination by GPS and Lidar and yields a consistent height datum for Tahiti and Moorea. The new Bouguer anomalies show gravity highs and lows in the centers and land-sea zones of the two islands, allowing further studies of the density structure and volcanism in the region.

  4. The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

    SciTech Connect

    Blakely, Richard J.; Sherrod, Brian; Weaver, Craig; Wells, Ray E.; Rohay, Alan C.

    2013-11-13

    Magnetic and gravity data, collected in south-central Washington near the Yakima Fold and Thrust Belt (YFTB) are used to model upper crustal structure, the extent of the late Columbia River Basalt flow named the Ice Harbor member, the vertical conduits (dikes) that the Ice Harbor erupted from, and whether the dikes are offset or affected by faulting on the Wallula Fault zone.

  5. Gravity anomalies near the east Pacific rise with wavelengths shorter than 3300 km recovered from GEOS-3/ATS-6 satellite-to-satellite Doppler tracking data

    NASA Technical Reports Server (NTRS)

    Marsh, J. G.; Marsh, B. D.; Conrad, T. D.; Wells, W. T.; Williamson, R. G.

    1977-01-01

    The velocity of the GEOS-3 satellite measured by Doppler as a function of time from the ATS-6 satellite was used to recover gravity anomalies in the region of the East Pacific. The orbit GEOS-3 at an altitude of 840 km was perturbed by spatial changes in Earth's gravitational field. These perturbations were measured via ATS-6 which is in a synchronous orbit at an altitude of about 40,000 km. The range-rate data were reduced using a gravitational field model complete to the 12 degree and order. A simulation of the possible effects causing the remaining range-rate residuals relative to the 12, 12 field shows that in general the dominant effect is the neglect of the higher degree and order coefficients of the gravitational field model.

  6. Monitoring Earthquake Fault Slip from Space: Model Implications for a High Precision, High Resolution Dedicated Gravity Mission (Invited)

    NASA Astrophysics Data System (ADS)

    Rundle, J. B.; Sachs, M. K.; Tiampo, K. F.; Fernandez, J.; Turcotte, D. L.; Donnellan, A.; Heien, E. M.; Kellogg, L. H.

    2013-12-01

    Monitoring deformation produced by slip on earthquake faults can be carried out via GPS or InSAR measurements. Both of these types of observations have their advantages and disadvantages, in terms of cost, availability, and technical difficulty. It has been suggested that another method to accomplish many of the same objectives would be via a dedicated gravity mission. The GRACE mission has shown that it is possible to make detailed gravity measurements from space for climate dynamics and other purposes. An important question is what level of accuracy will be needed for precise estimation of fault slip in earthquakes of interest to researchers. To answer this question, we turn to numerical simulations of earthquake fault systems and use these to estimate gravity changes. Rundle (1978) considered the question of gravity changes from dilation sources and thrust faults, and found that gravity changes in these cases were free air anomaly (dilation) and Bouguer anomaly (thrust fault). Walsh and Rice (1978) computed these by a different method and found the same result. Okada (1991) listed gravity and potential Green functions for all possible sources for the general case. Hayes et al (2006) then took the Okada Greens functions and applied them computed from an earlier version of Virtual California earthquake fault system simulations. Those simulations only involved vertical strike slip faults. The current far more advanced generation of Virtual California simulations involves faults of any orientation, dip, and rake. In this talk, we discuss these computations and the implications they have for accuracies needed for a dedicated gravity monitoring mission. Preliminary results are in agreement with previous results from Hayes et al (2006). Computed gravity changes are in the range of tens to hundreds of microgals over distances of few to many tens of kilometers. These values are presumably well within the range of measurement for a modern gravity mission flown either at

  7. Polyhedral shape model for terrain correction of gravity and gravity gradient data based on an adaptive mesh

    NASA Astrophysics Data System (ADS)

    Guo, Zhikui; Chen, Chao; Tao, Chunhui

    2016-04-01

    Since 2007, there are four China Da yang cruises (CDCs), which have been carried out to investigate polymetallic sulfides in the southwest Indian ridge (SWIR) and have acquired both gravity data and bathymetry data on the corresponding survey lines(Tao et al., 2014). Sandwell et al. (2014) published a new global marine gravity model including the free air gravity data and its first order vertical gradient (Vzz). Gravity data and its gradient can be used to extract unknown density structure information(e.g. crust thickness) under surface of the earth, but they contain all the mass effect under the observation point. Therefore, how to get accurate gravity and its gradient effect of the existing density structure (e.g. terrain) has been a key issue. Using the bathymetry data or ETOPO1 (http://www.ngdc.noaa.gov/mgg/global/global.html) model at a full resolution to calculate the terrain effect could spend too much computation time. We expect to develop an effective method that takes less time but can still yield the desired accuracy. In this study, a constant-density polyhedral model is used to calculate the gravity field and its vertical gradient, which is based on the work of Tsoulis (2012). According to gravity field attenuation with distance and variance of bathymetry, we present an adaptive mesh refinement and coarsening strategies to merge both global topography data and multi-beam bathymetry data. The local coarsening or size of mesh depends on user-defined accuracy and terrain variation (Davis et al., 2011). To depict terrain better, triangular surface element and rectangular surface element are used in fine and coarse mesh respectively. This strategy can also be applied to spherical coordinate in large region and global scale. Finally, we applied this method to calculate Bouguer gravity anomaly (BGA), mantle Bouguer anomaly(MBA) and their vertical gradient in SWIR. Further, we compared the result with previous results in the literature. Both synthetic model

  8. Doubling of states, quantum anomalies, and possible cosmological consequences in the continuum limit of the theory of discrete quantum gravity

    SciTech Connect

    Vergeles, S. N.

    2008-01-15

    The problem of the doubling of states is investigated in the framework of the theory of discrete quantum gravity under the assumption that the theory has a continuum (macroscopic) limit. It is demonstrated that irregular (in some sense) modes of fields (i.e., modes that change abruptly on scales of a lattice step and have a finite energy when the lattice step tends to zero) are separated from the normal modes. Some cosmological consequences of this finding are discussed.

  9. Software Analysis of New Space Gravity Data for Geophysics and Climate Research

    NASA Technical Reports Server (NTRS)

    Deese, Rupert; Ivins, Erik R.; Fielding, Eric J.

    2012-01-01

    Both the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellites are returning rich data for the study of the solid earth, the oceans, and the climate. Current software analysis tools do not provide researchers with the ease and flexibility required to make full use of this data. We evaluate the capabilities and shortcomings of existing software tools including Mathematica, the GOCE User Toolbox, the ICGEM's (International Center for Global Earth Models) web server, and Tesseroids. Using existing tools as necessary, we design and implement software with the capability to produce gridded data and publication quality renderings from raw gravity data. The straight forward software interface marks an improvement over previously existing tools and makes new space gravity data more useful to researchers. Using the software we calculate Bouguer anomalies of the gravity tensor's vertical component in the Gulf of Mexico, Antarctica, and the 2010 Maule earthquake region. These maps identify promising areas of future research.

  10. The Lunar Crustal Thickness from Analysis of the Lunar Prospector Gravity and Clementine Topography Datasets

    NASA Technical Reports Server (NTRS)

    Asmar, S.; Schubert, G.; Konopliv, A.; Moore, W.

    1999-01-01

    The Lunar Prospector spacecraft has mapped the gravity field of the Moon to a level of resolution never achieved before, and a spherical harmonic representation to degree and order 100 is available. When combined with the topography dataset produced by the Clementine mission, the resulting Bouguer anomaly map is interpreted to model the thickness of the lunar crust. Such models are crucial to understanding the lunar thermal history and the formation of geological features such as mascon basins, several more of which have been newly discovered from this dataset. A two-layer planetary model was used to compute the variations of the depth to the lunar Moho. The thickness values ranged from near 0 to 120 km. There is significant agreement with previous work using the Clementine gravitational field data with differences in specific locations such as South Pole-Aitken Basin, for example.

  11. Detailed gravity and aeromagnetic surveys of the Cove Fort-Sulphurdale KGRA and vicinity, Millard and Beaver Counties, Utah. Topical report

    SciTech Connect

    Cook, K.L.; Serpa, L.F.; Pe, W.

    1980-01-01

    A detailed gravity survey (comprising 231 stations over about 900 km/sup 2/) was made in the Cove Fort-Sulphurdale Known Geothermal Resource area (KGRA) and vicinity, Millard and Beaver counties, Utah to assist in the appraisal of the potential of this area as a geothermal resource. The survey reinforced the results and information obtained in the previous regional gravity surveys comprising 522 stations. The gravity data from about 700 stations were reduced and compiled as a terrain-corrected (out to 20 km) Bouguer gravity anomaly map with 1-mgal contour interval. In August 1975, an aeromagnetic survey was flown over part of the survey area at a constant barometric elevation of 12,000 ft (3660 m). These aeromagnetic data are used to supplement the interpretation of the gravity data. The aeromagnetic field intensity residual anomaly map and the second-order polynomial residual aeromagnetic map (obtained by removing a second-order polynomial surface) are presented with a 20-gamma contour interval. Two north-south profiles and one east-west profile were selected for magnetic interpretative modeling. The two north-south profiles were also stacked and averaged over 6-km-wide strips and modeled. The occurrences of hydrothermal alteration, hot spring deposits, and flowing hot springs coincide with inferred fault zones. No evidence of extensive alteration can be interpreted from the magnetic data.

  12. Internal architecture of the Tuxtla volcanic field, Veracruz, Mexico, inferred from gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Espindola, Juan Manuel; Lopez-Loera, Hector; Mena, Manuel; Zamora-Camacho, Araceli

    2016-09-01

    The Tuxtla Volcanic Field (TVF) is a basaltic volcanic field emerging from the plains of the western margin of the Gulf of Mexico in the Mexican State of Veracruz. Separated by hundreds of kilometers from the Trans-Mexican Volcanic Belt to the NW and the Chiapanecan Volcanic Arc to the SE, it stands detached not only in location but also in the composition of its rocks, which are predominantly alkaline. These characteristics make its origin somewhat puzzling. Furthermore, one of the large volcanoes of the field, San Martin Tuxtla, underwent an eruptive period in historical times (CE 1793). Such volcanic activity conveys particular importance to the study of the TVF from the perspective of volcanology and hazard assessment. Despite the above circumstances, few investigations about its internal structure have been reported. In this work, we present analyses of gravity and aeromagnetic data obtained from different sources. We present the complete Bouguer anomaly of the area and its separation into regional and residual components. The aeromagnetic data were processed to yield the reduction to the pole, the analytic signal, and the upward continuation to complete the interpretation of the gravity analyses. Three-dimensional density models of the regional and residual anomalies were obtained by inversion of the gravity signal adding the response of rectangular prisms at the nodes of a regular grid. We obtained a body with a somewhat flattened top at 16 km below sea level from the inversion of the regional. Three separate slender bodies with tops 6 km deep were obtained from the inversion of the residual. The gravity and magnetic anomalies, as well as the inferred source bodies that produce those geophysical anomalies, lie between the Sontecomapan and Catemaco faults, which are proposed as flower structures associated with an inferred deep-seated fault termed the Veracruz Fault. These fault systems along with magma intrusion at the lower crust are necessary features to

  13. Wisconsin gravity minimum: Solution of a geologic and geophysical puzzle and implications for cratonic evolution

    SciTech Connect

    Allen, D.J.; Hinze, W.J. )

    1992-06-01

    An intense Bouguer gravity anomaly minimum extending across much of Wisconsin cannot be explained by the surface Phanerozoic sedimentary strata, the basement Precambrian geology, or the topography of the region. The most intense ({minus}100 mgal) part of the minimum coincides with the 1.47 Ga anorogenic granitic Wolf River batholith of northeastern Wisconsin. In southern Wisconsin, however, the densities of the Precambrian basement rocks, which are older than the batholith, provide no clue to the origin of the anomaly. The gradients of the minimum indicate that the source of the anomaly is in the upper crust. Furthermore, nearby deep seismic reflection data indicate that lower crustal structures do not significantly contribute to the gravity minimum. Thus, the minimum is appropriately interpreted as originating from the low-density Wolf River batholith that crops out only in northeastern Wisconsin but is buried beneath a veneer of older rocks in the southern and central parts of the state. Gravity modeling suggests that the batholith is at least 10 km thick and encompasses an area of {approximately}50,000 km{sup 2}. This interpretation provides an important clue to the origin of similar negative gravity anomalies of the Phanerozoic strata-covered craton. Also, the presence of this massive granitic body appears to have influenced the evolution of the craton - e.g., by controlling the location of the 1.1 Ga Midcontinent rift system and the Paleozoic Wisconsin arch. The fact that the Wolf River batholith is mostly buried suggests that central Wisconsin has been tectonically stable for the past 1.47 b.y. and that the Precambrian basement has been minimally eroded.

  14. Magsat equivalent source anomalies over the southeastern United States - Implications for crustal magnetization

    NASA Technical Reports Server (NTRS)

    Ruder, M. E.; Alexander, S. S.

    1986-01-01

    The Magsat crustal anomaly field depicts a previously-unidentified long-wavelength negative anomaly centered over southeastern Georgia. Examination of Magsat ascending and descending passes clearly identifies the anomalous region, despite the high-frequency noise present in the data. Using ancillary seismic, electrical conductivity, Bouguer gravity, and aeromagnetic data, a preliminary model of crustal magnetization for the southern Appalachian region is presented. A lower crust characterized by a pervasive negative magnetization contrast extends from the New York-Alabama lineament southeast to the Fall Line. In southern Georgia and eastern Alabama (coincident with the Brunswick Terrane), the model calls for lower crustal magnetization contrast of -2.4 A/m; northern Georgia and the Carolinas are modeled with contrasts of -1.5 A/m. Large-scale blocks in the upper crust which correspond to the Blue Ridge, Charlotte belt, and Carolina Slate belt, are modeled with magnetization contrasts of -1.2 A/m, 1.2 A/m, and 1.2 A/m respectively. The model accurately reproduces the amplitude of the observed low in the equivalent source Magsat anomaly field calculated at 325 km altitude and is spatially consistent with the 400 km lowpass-filtered aeromagnetic map of the region.

  15. Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies

    NASA Astrophysics Data System (ADS)

    Shahraki, Meysam; Schmeling, Harro; Haas, Peter

    2016-04-01

    Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the thickness of lithospheric jumps and corresponding tectonic stress. We analysed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and reasonable assumptions about densities these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. They reveal a small asymmetry between the African and S-American crusts and lithospheres by a few kilometers. On both sides, the continental lithosphere is about 15 - 30km thicker than the oceanic lithosphere. To keep such geoid jumps stable over O(100Ma) fully dynamic models show that lithospheric viscosities must be of the order of 1e23 Pa s.

  16. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data

    NASA Astrophysics Data System (ADS)

    Andrews-Hanna, Jeffrey C.; Besserer, Jonathan; Head, James W., III; Howett, Carly J. A.; Kiefer, Walter S.; Lucey, Paul J.; McGovern, Patrick J.; Melosh, H. Jay; Neumann, Gregory A.; Phillips, Roger J.; Schenk, Paul M.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T.

    2014-10-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region.

  17. Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data.

    PubMed

    Andrews-Hanna, Jeffrey C; Besserer, Jonathan; Head, James W; Howett, Carly J A; Kiefer, Walter S; Lucey, Paul J; McGovern, Patrick J; Melosh, H Jay; Neumann, Gregory A; Phillips, Roger J; Schenk, Paul M; Smith, David E; Solomon, Sean C; Zuber, Maria T

    2014-10-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The region has been interpreted as an ancient impact basin approximately 3,200 kilometres in diameter, although supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border Procellarum and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dykes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of border structures in a quasi-rectangular pattern with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the greater-than-average heat flux in the region. PMID:25279919

  18. Structure and Evolution of the Lunar Procellarum Region as Revealed by GRAIL Gravity Data

    NASA Technical Reports Server (NTRS)

    Andrews-Hanna, Jeffrey C.; Besserer, Jonathan; Head, James W., III; Howett, Carly J. A.; Kiefer, Walter S.; Lucey, Paul J.; McGovern, Patrick J.; Melosh, H. Jay; Neumann, Gregory A.; Phillips, Roger J.; Schenk, Paul M.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T.

    2014-01-01

    The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The Procellarum region has been interpreted as an ancient impact basin approximately 3200 km in diameter, though supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border the Procellarum region and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dikes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of quasi-rectangular border structures with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the elevated heat flux in the region.

  19. Subsurface structure of the eastern edge of the Zagros basin as inferred from gravity and satellite data

    SciTech Connect

    Bushara, M.N.

    1995-09-01

    A data set of 10,505 points of land gravity measurements from southeast Iran obtained from the Bureau Gravimetrique International, combined with Landsat imagery, was used to investigate crustal and Cenozoic lithospheric structure. Interpretation of the Bouguer anomalies reveals three primary structural features. The Zagros Mountain belt is characterized by a progressive decrease in gravity values from -70 mGal near the Persian Gulf to -160 mGal over the structure zone between the Arabian margin and central Iran crustal blocks. The second feature is marked by a backward-L-shaped pair of anomalies that extends from the eastern peripheries of the Zagros basin and wraps around southern Iranian shores. These 15- to 20-km-deep source anomalies, with amplitudes of as much as 10 mGal, are interpreted as intrabasement intrusions demarcating an ancient rift axis. The shallow (6-8)km east-west-trending anomalies are perhaps interbasement uplifts bordered by reverse faults. The third structure, observed on both gravity and Landsat displays, a north-striking eastward-facing topographic escarpment, has a gravity gradient of 0.85 mGal/km, and is right laterally offset approximately 100 km, and is right laterally offset approximately 100 km by the Zagros main recent fault. A comparison of gravity features with surface structures on Thematic Mapper and Landsat Multi-spectral Scanner imagery indicates that a northeast-trending fault system is the result of post-Miocene pervasive transpressive stress coupled with clockwise rotation of underlying basement blocks following the collision of Arabia and Iran. Accommodation structures such as forced folds and {open_quotes}rabbit-ear{close_quotes} anticlines may develop over and on the flanks of the basement blocks, providing remigration and trapping mechanisms for new oil and gas plays.

  20. Gravity and thermal models for the twin peaks silicic volcanic center, Southwestern Utah

    SciTech Connect

    Carrier, D.L.; Chapman, D.S.

    1981-11-10

    Gravity, heat flow, and surface geology observations have been used as constraints for a thermal model of a late Tertiary silicic volcanic center at Twin Peaks, Utah. Silicic Volcanism began in the area with the extrusion of the Coyote Hills rhyolite 2.74 +- 0.1 m.y. ago, followed by the Cudahy Mine obsidian, felsite, and volcanoclastics, and finally by a complex sequence of domes and flows that lasted until 2.3 +- 0.1 m.y. ago. Basalt sequence span the time 2.5 to 0.9 m.y. Terrain-corrected Bouguer gravity anomalies at Twin Peaks are shaped by three features of varying characteristic dimensions: (1) a major north-northeast trending --30 mGal gravity trough roughly 40 km wide caused by a thick sequence of Cenozoic sediments in the Black Rock Desert Valley, (2) a local roughly circular -7 mGal gravity low, 26 km across, probably related to an intrusive body in the basement, and (3) a series of narrow positive anomalies up to + 10 mGal produced by the major Twin Peaks volcanic domes. The intrusive bodies have been modeled as three-dimensional vertical cylinders; the total volume of intrusive material is estimated to be about 500 km/sup 3/. Simple models, assuming conductive heat transfer and using geometrical constraints from the gravity results, predict that a negligible thermal anomaly should exist 1 m.y. after emplacement of the intrusion. This prediction is consistent with an average heat flow of 96 mW m/sup -2/ for the area, not significantly different from eastern Basin and Range values elsewhere. Magmatic longevity of this system 2.7 to 2.3 m.y. for silicic volcanism of 2.5 to 0.9 m.y. for basaltic volcanism, does not seem to prolong the cooling of the system substantially beyond that predicted by conductive cooling.

  1. Local Gravity Field Determination On The Moon Using GRAIL Extended Mission Data

    NASA Astrophysics Data System (ADS)

    Goossens, S. J.; Lemoine, F. G.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2013-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were launched on September 10, 2011, and conducted their primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km. GRAIL's extended mission commenced on August 30 and was completed on December 14, 2012. The average altitude during the extended mission was 23 km above lunar surface. Both primary and extended mission data have been processed at NASA/GSFC using the GEODYN software, resulting in high-resolution (degree and order 900 in spherical harmonics) gravity field models of high accuracy. However, especially during low-altitude passes, Ka-band range-rate (KBRR) data residuals are still well above noise level. Here, we focus on methods to determine local gravity adjustments from KBRR data. We represent gravity in the area of interest as gravity anomaly adjustments with respect to the background spherical harmonics model. We use KBRR data only over the area of interest, and we then perform short-arc orbit determination. Our areas of focus are mainly the Mare Orientale area, where GRAIL achieved its lowest altitude above the lunar surface towards the end of the mission, and the south pole area, where naturally there is a confluence of orbit tracks. We investigate different grids and different smoothing constraints used in the estimation of the anomalies, numerical differentiation with respect to time of the KBRR data to localize its sensitivity further, and we evaluate the solutions in terms of Bouguer anomaly signatures, KBRR data fit, and correlations with local topography.

  2. High-resolution global and local lunar gravity field models using GRAIL mission data

    NASA Astrophysics Data System (ADS)

    Goossens, S. J.; Lemoine, F. G.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Loomis, B.; Chinn, D. S.; Smith, D. E.; Zuber, M. T.

    2014-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were designed to map the structure of the Moon through high-precision global gravity mapping. The mission consisted of two spacecraft with Ka-band inter-satellite tracking complemented by tracking from Earth. The mission had two phases: (1) a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km; (2) an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and between 11-20 km through December 14. Both the primary and the extended mission data have been processed into global models of the lunar gravity field at NASA/GSFC using the GEODYN software. Here we present our latest global model, an expansion in spherical harmonics of degree and order 1080. We discuss this new solution in terms of its power spectrum, its free-air and Bouguer anomalies, its associated error spectrum, and its correlations with topography-induced gravity. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale and the south pole area. We express gravity in terms of anomalies, and estimate them with respect to a global background model. We apply neighbor-smoothing in our estimation procedure. We present a local solution over the south pole area in a resolution of 1/6 by 1/6 of a degree, equivalent to degree and order 1080, and we compare this local solution to our global model.

  3. Three-dimensional density structures of Taiwan and tectonic implications based on the analysis of gravity data

    NASA Astrophysics Data System (ADS)

    Hsieh, Hsien-Hsiang; Yen, Horng-Yuan

    2016-07-01

    Taiwan is located in a collision and subduction area and has a complex tectonic history. To better understand the complicated structure beneath Taiwan, gravity studies, in addition to seismic and geological studies, provide useful geophysical information for studying shallow depths. Previous gravity studies of Taiwan in the last 30 years focused on local regionalized explanations and 2-D profile modeling. This study is the first to complete a 3-D gravity inversion of Taiwan, and it provides a more comprehensive and large-scale tectonic analysis. Following 3-D gravity inversion using the least squares method, we sliced horizontal and vertical profiles from the 3-D density model to visualize tectonic changes. The low Bouguer anomaly was caused by thick sediment and crust layers. The high-density layers are located in special tectonic areas such as the Peikang and Kuanying basement highs. The deepest Moho depth beneath the middle of the Central Range is 45-50 km. The high gradient changes of the eastern section of the Moho relief are shown by the complex mechanism of plate collision. The geometry of plate subduction is apparent in northeastern Taiwan, and the oceanic crust is observable under eastern Taiwan, showing arc-collision boundaries. Our 3-D density model, when combined with updated gravity data and seismic tomography, offers better resolution for deep structures than the previous 2-D forward results and serves as a physical property reference to better understand the tectonic structure beneath Taiwan.

  4. Gravity Data from the Teboursouk Area ("Diapirs Zone", Northern Tunisia): Characterization of Deep Structures and Updated Tectonic Pattern

    NASA Astrophysics Data System (ADS)

    Hachani, Fatma; Balti, Hadhemi; Kadri, Ali; Gasmi, Mohamed

    2016-04-01

    Located between eastern segments of the Atlas and Tell-Rif orogenic belts, the "Dome zone" of northern Tunisia is characterized by the juxtaposition of various structures that mainly controlled the long geodynamic history of this part of the south-Tethyan Margin. To better understand the organization and deep extension of these structures, gravity data from the Teboursouk key area are proposed. These data include the plotting of Bouguer anomaly map and related parameters such as vertical and horizontal gradients, upward continuation and Euler solution. Compared to geological and structural maps available, they allow the identification of new deep structures and greater precision regarding the characteristics and organization of known ones; consequently, an updated structural pattern is proposed.

  5. Detailed gravity mapping of the Panther Mountain circular structure, Catskill Mountains, New York

    SciTech Connect

    Isachsen, Y.W. ); Revetta, F.A. )

    1993-03-01

    The Panther Mountain circular structure is located in the Catskill Mountains near the eastern edge of the Allegheny Plateau where depth through the sedimentary section to basement is about 3200 m. The structure is distinguished from the rest of the Plateau only by its physiography. It is a circular mountain mass, 10 km in diameter, defined by an anomalous annular drainage pattern formed by Esopus Creek and its tributary Woodland Creek. Because of pervasive fluvial cross bedding in the sedimentary pile, the authors were unable to determine whether the structure is slightly domical, sightly basinal, or unwarped. North-south and east-west gravity profiles were next made and modeled to look for a subsurface explanation for the structure. The only computed profiles that matched the measured values were those for a shallowly-buried meteorite crater with its underlying breccia lens, lying beneath the Panther Mountain. Renewed interest in the structure led them to make 125 new gravity measurements, in a study that is continuing. Gravity values are corrected using the International Gravity Formula of 1967 and densities of 2.67 and 2.50 gms/cm[sup 3]. Terrain corrections were computed using an inner radius of .895 km and an outer radius of 166.70 km. The complete Bouguer gravity anomaly was separated into its regional and residual components to obtain a third order residual gravity map for computer modeling. The residual gravity map confirms the earlier detected gravity low and leaves the buried meteorite crater model as a viable model.

  6. The influence of pre-existing structures on the evolution of the southern Kenya Rift Valley — evidence from seismic and gravity studies

    NASA Astrophysics Data System (ADS)

    Birt, C. S.; Maguire, P. K. H.; Khan, M. A.; Thybo, H.; Keller, G. R.; Patel, J.

    1997-09-01

    The Kenya Rift is an active continental rift that has developed since the Late Oligocene. Although a thermal origin for the rifting episode is indicated by the scale of volcanism and its relative timing with uplift and faulting, the influence of pre-existing lithospheric structural controls is poorly understood. The interpretation of a 430-km-long seismic refraction and gravity line across the southern part of the Kenya Rift shows that the rift is developed across a transition zone, thought to represent the sheared Proterozoic boundary between the Archaean Nyanza Craton and the mobile Mozambique Belt. This zone of weakness has been exploited by the recent thermal rifting event. The Moho is at a depth of 33 km beneath the Archaean craton in the western part of the profile, and 40 km beneath the Mozambique Belt in the east. A few kilometres of localised crustal thinning has developed across the transition from thin to thick crust. At the surface, brittle faulting has formed an asymmetric rift basin 3.6 km deep, filled with low-velocity volcanic rocks. Basement velocities show a transition across the same area from low velocities (6.0 km s -1) in the Archaean, to high velocities (6.35 km s -1) in the Proterozoic. Mid-crustal layers show no deformation that can be attributed to the rifting event. Poorly constrained upper mantle velocities of 7.8 km s -1 beneath the southern rift confirm the continuation of the axial low-velocity zone imaged in previous seismic experiments. This is interpreted as the effect of small degrees of partial melt caused by elevated mantle temperatures. Gravity modelling suggests a contribution to the Bouguer anomaly from below the Moho, invoking the need for deep density contrasts. The regional gravity gradient necessary to model the Bouguer anomaly is used as supporting evidence for mantle-plume type circulation beneath the uplifted East African Plateau to the west of the Kenya Rift.

  7. Analysis of Marine Gravity Anomalies in the Ulleung Basin (East Sea/Sea of Japan) and Its Implications for the Architecture of Rift-Dominated Backarc Basin

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Mook; Kim, Yoon-Mi

    2016-04-01

    Marginal basins locate between the continent and arc islands often exhibit diverse style of opening, from regions that appear to have formed by well-defined and localized spreading center (manifested by the presence of distinct seafloor magnetic anomaly patterns) to those with less obvious zones of extension and a broad magmatic emplacement most likely in the lower crust. Such difference in the style of back-arc basin formation may lead to marked difference in crustal structure in terms of its overall thickness and spatial variations. The Ulleung Basin, one of three major basins in the East Sea/Sea of Japan, is considered to represent a continental rifting end-member of back-arc opening. Although a great deal of work has been conducted on the sedimentary sections in the last several decades, the deep crustal sections have not been systematically investigated for long time, and thus the structure and characteristics of the crust remain poorly understood. This study examines the marine gravity anomalies of the Ulleung Basin in order to understand the crustal structure using crucial sediment-thickness information. Our analysis shows that the Moho depth in general varies from 16 km at the basin center to 22 km at the margins. However, within the basin center, the inferred thickness of the crust is more or less the same (10-12 km), thus by varying only about 10-20% of the total thickness, contrary to the previous impression. The almost-uniformly-thick crust that is thicker than a normal oceanic crust (~ 7 km) is consistent with previous observations using ocean bottom seismometers and recent deep seismic results from the nearby Yamato Basin. Another important finding is that small residual mantle gravity anomaly highs exist in the northern part of the basin. These highs are aligned in the NNE-SSW direction which correspond to the orientation of the major tectonic structures on the Korean Peninsula, raising the possibility that, though by a small degree, they are a

  8. Local Lunar Gravity Field Analysis over the South Pole-aitken Basin from SELENE Farside Tracking Data

    NASA Technical Reports Server (NTRS)

    Goossens, Sander Johannes; Ishihara, Yoshiaki; Matsumoto, Koji; Sasaki, Sho

    2012-01-01

    We present a method with which we determined the local lunar gravity field model over the South Pole-Aitken (SPA) basin on the farside of the Moon by estimating adjustments to a global lunar gravity field model using SELENE tracking data. Our adjustments are expressed in localized functions concentrated over the SPA region in a spherical cap with a radius of 45deg centered at (191.1 deg E, 53.2 deg S), and the resolution is equivalent to a 150th degree and order spherical harmonics expansion. The new solution over SPA was used in several applications of geophysical analysis. It shows an increased correlation with high-resolution lunar topography in the frequency band l = 40-70, and admittance values are slightly different and more leveled when compared to other, global gravity field models using the same data. The adjustments expressed in free-air anomalies and differences in Bouguer anomalies between the local solution and the a priori global solution correlate with topographic surface features. The Moho structure beneath the SPA basin is slightly modified in our solution, most notably at the southern rim of the Apollo basin and around the Zeeman crater

  9. Complete Bouguer gravity and aeromagnetic maps of the Rattlesnake Roadless Area, Missoula County, Montana

    USGS Publications Warehouse

    Kulik, Dolores M.

    1986-01-01

    The rocks in the study area consist mainly of the Helena Formation and the Missoula Group of the Belt Supergroup (Proterozoic Y).  Rock units of less importance are diabase sills and dikes of probable Proterozoic Z age, Middle Cambrian rocks, and glacial deposits.  Structurally, the study area consists of the Rattlesnake thrust system in the south part and a parautochthonous area broken by vertical faults in the north part.

  10. Heat flow in the Oregon Cascade Range and its correlation with regional gravity, Curie point depths, and geology

    SciTech Connect

    Blackwell, D.D.; Steele, J.L. ); Frohme, M.K. ); Murphey, C.F. ); Priest, G.R.; Black, G.L. )

    1990-11-10

    Heat flow measurements from several deep wells (up to 2,500 m deep), as well as extensive new data from industry exploration efforts in the Breitenbush and the Santiam Pass-Belknap/Foley areas are described. The heat flow is about 100 mW m{sup {minus}2} in the High Cascade Range and at the eastern edge of the Western Cascade Range, and about 40-50 mW m{sup {minus}2} to the west in the outer arc block of the subduction zone. The gravity field in the Cascade Range has characteristics that can be closely related to the heat flow pattern. The relationship may be causal, and to examine the relationship in more detail, earlier two-dimensional modeling is extended to three dimensions. Consideration of the effects of a midcrustal density anomaly, such as might be associated with a region with at least areas of partial melt, as two major consequences. The first of these is that a high-frequency gravity gradient near the Western Cascade Range/High Cascade Range boundary is explained. Second, the negative gravity anomaly associated with the northeast/southwest striking regional Bouguer gravity anomaly associated with the north edge of the Blue Mountains becomes continuous across the Cascade Range with a similar feature along the north side of the Klamath Mountains. The correlation, or lack thereof, of the heat flow, depth to Curie point, gravity field, crustal electrical resistivity, crustal seismic velocity, and geology in the High/Western Cascade Ranges is summarized.

  11. Improving the terrestial gravity dataset in South-Estonia

    NASA Astrophysics Data System (ADS)

    Oja, T.; Gruno, A.; Bloom, A.; Mäekivi, E.; Ellmann, A.; All, T.; Jürgenson, H.; Michelson, M.

    2009-04-01

    The only available gravity dataset covering the whole of Estonia has been observed from 1949 to 1958. This historic dataset has been used as a main input source for many applications including the geoid determination, the realization of the height system, the geological mapping. However, some recent studies have been indicated remarkable systematic biases in the dataset. For instance, a comparison of modern gravity control points with the historic data revealed unreasonable discrepancies in a large region in South-Estonia. However, the distribution of the gravity control was scarce, which did not allow to fully assess the quality of the historic data in the study area. In 2008 a pilot project was called out as a cooperation between Estonian Land Board, Geological Survey of Estonia, Tallinn University of Technology and Estonian University of Life Sciences to densify the detected problematic area (about 2000 km2) with new and reliable gravity data. Field work was carried out in October and November 2008, whereas GPS RTK and relative Scintrex gravimeter CG5 were used for precise positioning and gravity determinations, respectively. Altogether more than 140 new points were determined along the roads. Despite bad weather conditions and unstable observation base of the gravimeter (mostly on the bank of the road), uncertainty better than ±0.1 mGal (1 mGal = 10-5 m/s2) was estimated from the adjustment of gravimeter's readings. The separate gravity dataset of the Estonian Geological Survey were also incorporated into the gravity database of the project for further analysis. Those data were collected within several geological mapping projects in 1981-2007 and contain the data with uncertainty better than ±0.25 mGal. After the collection of new gravity data, a Kriging with proper variogram modeling was applied to form the Bouguer anomaly grids of the historic and the new datasets. The comparison of the resulting grids revealed biases up to -4 mGal at certain regions

  12. Vertical density contrast and mapping of basement, Conrad and Moho morphologies through 2D spectral analysis of gravity data in and around Odisha, India

    NASA Astrophysics Data System (ADS)

    Kumar, Arbind; S. Roy, P. N.; Das, L. K.

    2016-07-01

    Power spectrum analysis of Complete Bouguer Anomaly (CBA) map of Eastern Ghat Mobile Belt (EGMB) and its surroundings in India through Two Dimensional (2D) spectral analysis has provided estimates of the ensemble average depths for the density discontinuities which represent crustal inhomogeneities. The spectral analysis method has helped to estimate the depths of a perturbing body sources which are obtained from the negative slopes of the linear relationship between the logarithmic power spectrum and the wave-numbers of the gravity field. The detailed analysis reveals three horizontal discontinuities (i) Phanerozoic sediment thickness (ii) Basement depth and (iii) Conrad discontinuity. The average thickness of Phanerozoic sediments is estimated to be 3 km whereas depth of basement and Conrad discontinuity are at 7 km and 14.5 km respectively. Additionally Mohorovicic discontinuity also estimated at a depth of 32.8 km in the study region.

  13. Relation of Topography to Airborne Gravity in Afghanistan and the Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Jung, W.; Brozena, J. M.; Peters, M. F.

    2012-12-01

    As part of a multi-sensor, multi-disciplinary aerogeophysical survey, the US Naval Research Laboratory collected airborne gravity over most of Afghanistan in 2006 (http://pubs.usgs.gov/of/2008/1089/Afghan_grv.html). The data were measured using a pair of ZLS Corporation air-sea gravimeters 7 km altitude above mean sea level aboard an NP-3D Orion aircraft operated by the US Navy's Scientific Development Squadron One (VXS-1). Aircraft positions were determined from kinematic GPS measurements in the aircraft relative to five base stations using differential interferometric techniques. Track spacing was set to 4 km over much of Afghanistan, but was increased to 8 km in the northern block of the survey area. Aircraft ground speed averaged between 300 and 380 knots, faster than ideal for high resolution gravity, but enabled approximately 113,000-km of data tracks to be flown in 220 flight hours, covering more than 330000 km2. In this presentation, we investigate the implications of the airborne gravity data for the tectonic development history of Afghanistan. Afghanistan is described as comprising three different platforms (Wheeler et al., 2005): 1) the north Afghanistan platform north of the Hari-Rud fault (HRF), a part of the Eurasian plate for 250-350 my; 2) the accreted terranes south of the HRF including low flats, formed as island arcs and fragments of continental and oceanic crust collided with the Eurasian plate during the closure of the Tethys Ocean in the past 250 my; and 3) the transpressional plate in the east, formed as the Indian plate moves northward since Cretaceous. The Bouguer anomaly map reveals elongated negative values along the east-west striking HRF, which seems to manifest different tectonic developmental histories across the boundary. Over the southern flats in the accreted terranes platform, the Bouguer anomaly map appears to show a continuation of alternating southwest-northeast trending highs and lows like those over the northern high

  14. Investigation of the geologic and tectonic structures of Bafa Lake and Akbuk Gulf (terrestrial and marine areas) by means of gravity and magnetic methods

    NASA Astrophysics Data System (ADS)

    Edremit, Şüheda; Özel, Erdeniz

    2016-04-01

    Geologic units of Bafa Lake and Akbuk Gulf, which have very importance in point of geologic and tectonic structure, are generally are classified by high-grade metamorphic units of the Menderes Core Complex, Cycladic Complex (schist, marble, eclogite), Afyon zone meta sedimentary and Pan-African basement rocks, Neogene volcanic-sedimentary rocks and alluvium. As for tectonic structures of study areas are; Izmir-Balikesir Transfer Zone also affected the Buyuk Menderes Graben, Bornova Flysch Zone, Menderes Massif and Lycian Nappes. Regional researches were studied to reveal using Turkey Bouguer Anomaly and Turkey Aeromagnetic regional map with gravity method used for geologic structures analysis and magnetic method used to explain main structure, tectonic conditions of underground. General geologic structure and tectonic lineaments of region were examined and interpretated compatibility with gravity and magnetic values. When the geologic and tectonic structures on the terrestrial areas are generally investigated, graben systems and linearities are clearly seen on the Bouguer Anomaly map. Positive values are seen in the Bornova Flysch Zone and Menderes Massif areas at the north of study areas arising from high-density ophiolitic and metamorphic units. Graben areas in the Menderes Massif are observed negative gravity values on the low-density young alluviums. Positive gravity values are increased up to 50-60 mgal on the metamorphic rocks that are named Cycladic Complex located southwest of study areas. At the aeromagnetic regional magnetic map, gamma values about -100 observed on the Menderes Massif region are indicated metagranite rocks that are Paleozoic crystalline structure. Gamma values, which are changed between -100 and +100 at the transition areas granite with schists, are obviously revealed this transition region. Located northwest of study areas Upper Miocene-Pliocene aged from sedimentary rocks on the terrestrial carbonates and nonsegregated terrestrial

  15. Prediction of sediment thickness in the Norwegian-Greenland Sea from gravity inversion

    NASA Astrophysics Data System (ADS)

    Engen, Øyvind; Frazer, L. Neil; Wessel, PâL.; Faleide, Jan Inge

    2006-11-01

    We explore the feasibility of inverting freely available altimetry-derived gravity grids for sediment thickness on oceanic crust. A four-layer Earth model is adopted, assuming that the gravity signal from the base of the sedimentary layer can be fully isolated from the observed free-air gravity. The following additional data are required: (1) shipboard bathymetry for reliable Bouguer correction, (2) oceanic crustal ages to correct for gravity anomalies related to the thermal history of lithospheric breakup and seafloor spreading, and (3) some wide-angle seismic observations of sediment thickness. A fixed relationship between the base of the sedimentary layer and the Moho is also required because of limited gravity resolution at large depths. The final inversion setup searches for three control parameter values (density of uppermost sediments, density of oceanic crystalline crust, and thermal diffusivity of mantle rock) that minimize misfit between the Earth model and observations. Applied to the Norwegian-Greenland Sea, the inversion successfully predicts locations of >20-25 km wide depocenters and crystalline crustal highs, yet ˜1 km thickness errors are common even in well-constrained areas. The largest errors are associated with underplated crust, active mid-ocean ridges, and the continent-ocean boundary, indicating locally incorrect assumptions of mantle thermal structure and crystalline crustal thickness. The thicknesses of >4 km thick submarine fans are underpredicted, probably because of too low sedimentary densities in the Earth model. If these limitations are acceptable or do not apply because of simple crustal structure, gravity inversion may be used for mapping regional sedimentary patterns, e.g., in the Arctic Ocean.

  16. Detailed gravity survey over a known carbonate reef (Devonian) in Williston basin

    SciTech Connect

    Braun, S.M.

    1988-07-01

    A detailed gravity study, conducted over the Shell Golden carbonate reef located in the Winnipegosis Formation (Devonian) of the Williston basin in north-central North Dakota, indicates a massive carbonate platform with several interconnected vertical accumulations, perhaps pinnacle in nature, from this platform. This reef is found at a depth of about 2400 m (8000 ft). Because elevations and north-south positions were surveyed to /+-/3 cm (0.1 ft) and /+-/ 1 (3.3 ft), respectively, an accuracy of 0.01 mgal was obtained. Five profiles were made: three lines running east-west and two lines running north-south, forming a grid pattern over the reef. The distance between each line was 1.6 km (1.0 mi) with gravity-station spacing along each line being 0.4 km (0.25 mi). The Golden reef and most reefs of this nature throughout the North Dakota portion of the Williston basin have been interpreted to be isolated pinnacles with physical dimensions about 60-75 m (200-250 ft) thick and 0.8 km (0.5 mi) in basal diameter. However, analysis of the residual Bouguer gravity anomalies (0.2-0.5 mgal) obtained from this study indicates this reef is more complex than previously thought. The maximum thicknesses of the complex are on the order of 120-185 m (400-600 ft) with compaction anticlines also contributing to the total gravity anomaly. The modeled reef complex extends in a northeast-southwest direction and probably extends beyond the study area along that line.

  17. 3D gravity modeling of the Corrientes province (NE Argentina) and its importance to the Guarani Aquifer System

    NASA Astrophysics Data System (ADS)

    Mira, Andrés; Gómez Dacal, María Laura; Tocho, Claudia; Vives, Luis

    2013-11-01

    This paper presents a geological model of Corrientes province (Argentina) based on Bouguer gravity anomaly data, obtained in 2073 measurement points. To build the model, the IGMAS + interactive program was used. Two areas of approximately 135,000 km2 were modeled in this study. The selection of these areas was based on the sectors where the largest number of gravity anomaly measurements was made and other type of data was available to perform the parameterization (i.e, lithology profiles in boreholes, seismic profiles and audio-magnetotelluric AMT soundings). The initial geological configuration proposed was composed by four layers: basement, sediments (Paleozoic-Lower Cretaceous), basalts (Serra Geral Group, Lower Cretaceous) and post-basaltic sediments. The result shows a basement compartmentalized in structural blocks separated by large faults. The connection of Asunción and Río Grande Arches is confirmed along a structural high that crosses Corrientes province from SE to NW. The basaltic layer shows lateral changes in its thickness, due to faulting, almost disappearing on the NW of Corrientes. This structural configuration has a special hydrogeological importance because it produces the rise of the Guaraní Aquifer System sedimentary series near the surface and the intense fracture network makes this area prone to local recharge and regional discharge.

  18. Crustal thickness variation from a continental to an island arc terrane: Clues from the gravity signatures of the Central Philippines

    NASA Astrophysics Data System (ADS)

    Manalo, Pearlyn C.; Dimalanta, Carla B.; Faustino-Eslava, Decibel V.; Ramos, Noelynna T.; Queaño, Karlo L.; Yumul, Graciano P.

    2015-05-01

    Offshore and ground gravity data were utilized to estimate crustal thickness across the Central Philippines where a transition from continental to island arc terrane occurs. Significant differences in gravity anomalies were observed between the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB), two major terranes that came together through arc-continent collision. Islands of the PCB (Mindoro, Tablas, Romblon, Sibuyan and western Panay), made up of an assortment of continent-derived sedimentary and igneous rocks and slivers of ophiolitic bodies, register lower Bouguer anomalies compared to that displayed by Masbate Island in the PMB. The calculated crustal thickness of this region exhibits a complex Moho topography of non-uniform depth across the collision zone with the thickest parts (∼32 km) corresponding with ophiolitic units emplaced consequent to arc-continent collision. On the other hand, relatively thinner crust (∼21 km) within the collision zone coincides with areas surmised to have undergone attenuation following intra-arc rifting. The same characteristics are observed offshore of western Mindoro and within the Marinduque Basin, areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra-basin openings.

  19. Gravity constraints on the geometry of the Big Bend of the San Andreas Fault in the southern Carrizo Plains and Pine Mountain egion

    NASA Astrophysics Data System (ADS)

    Altintas, Ali Can

    The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ?35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ?6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on

  20. Moho structure of the South China Sea basin and the surrounding from constrained 3-D gravity inversion

    NASA Astrophysics Data System (ADS)

    Zhaocai, W.; Jinyao, G.

    2014-12-01

    We have obtained the Moho depth of the South China Sea basin using gravity data with the 191 control points from seismic data and sonobuoys. To obtain the residual mantle Bouguer anomaly (RMBA), we deducted the anomaly from lateral changes in bathymetry or topography, the gravity anomaly due to changes in sediment thickness and density from the free air anomaly firstly, and then corrected the lithosphere thermal gravity anomaly from the rifted margin to the spread ridge. According to the relationship between the control points and RMBA, we calculated the initial Moho depth, from which, we done an iterative cycle of gravity inversion to predict the final Moho depth and crustal thickness. To calculate the lithosphere thermal gravity anomaly, we defined a critical thinning factor for the initiation of oceanic crust production, and a maximum oceanic crustal thickness; for this study area, values of 0.5 and 9 km were used respectively, consistent with the Moho depth of 20km and 14km respectively, with the initial thickness of continental crust of 32km. The RMS(root mean square) difference with the control points is 1.54km. Over most of the South China Sea basin, the Moho depth is 11 and 13km, the crustal thickness is 5-8km. The Moho depth of the Northwest sub basin has values between 12 and 13km, the crustal thickness is mostly ~7km. The NW trending fault divides obviously the extinct spreading centers of the East and southwest sub basin. Meanwhile, on the north side of the two sub basin extinct spreading centers, the crustal thickness is slightly thicker 1km than the south. The ocean-continent transition (OCT) is enclosed by the 14km and 20km Moho depth contour. At the East sub basin, the OCT shows asymmetry, and is broader and longer on the northern margin than the southern margin. One of the most noticeable characteristics in the northeastern margin of the OCT is that the crustal thickness is 10-16km. However, at the southwest sub basin, the OCT is symmetrical.

  1. Gravity and Magnetic Survey of the Oaxaca-Juarez Terrane Boundary (Oaxaca Fault), Southern Mexico: Evidence for three Half Grabens

    NASA Astrophysics Data System (ADS)

    Campos-Enriquez, J. O.; Belmonte-Jimenez, S. I.; Ortega-Gutierrez, F.; Keppie-Moorhouse, J. D.; Martinez-Silva, J.; Martinez-Serrano, R.

    2007-05-01

    A geophysical survey of the Oaxaca Fault boundary between the Oaxaca (Oaxaquia) (Zapoteco) and Juarez (Cuicateco) terranes along the Etla and Zaachila valleys area, southern Mexico shows a series of NW-SE Bouguer and magnetic anomalies with stronger gradients towards the east. The basement from the Oaxaca terrane has a high density (2.8 gr/cm3 ) and magnetic susceptibility of up to 0.0051 cgs units, which contrast with the Juarez basement that has a lower density (2.67 gr/cm3) and a higher magnetic susceptibility (values ranging between 0.0025 to 0.0045 cgs units). The magnetic susceptibility is similar south of the Donaji fault. Interpretation of six combined gravity and magnetic NE-SW profiles perpendicular to the valleys indicates the presence of a composite depression comprising three N-S sub-basins with the Etla and Zachila sub-basins located at the northern and southern portions, respectively, separated by a third sub-basin relatively displaced westwards. They are bounded on the east by the steeply W-dipping Oaxaca master fault, and on the west by the gently E-dipping Huitzo-Zimatlan fault. Two interpretations are suggested for the southward continuation of the Oaxaca Fault: 1) it continues southwards at depth with the same strike. Together the Bouguer and total field magnetic anomalies suggest that the Oaxaca fault is continuous from Etla via Oaxaca City and Ocotlán de Morelos probably to Miahuatlán de Porfirio Díaz, and 2) it continues with the same strike but is displaced eastwards ~20 km along a sinistral transfer fault, which forms the northern boundary of the Zaachila sub-basin.

  2. Gravity Survey of the Rye Patch KGRA, Rye Patch, Nevada

    NASA Astrophysics Data System (ADS)

    Mcdonald, M. R.; Gosnold, W. D.

    2011-12-01

    The Rye Patch Known Geothermal Resource Area (KGRA) is located in Pershing County Nevada on the west side of the Humboldt Range and east of the Rye Patch Reservoir approximately 200 km northeast of Reno, Nevada. Previous studies include an earlier gravity survey, 3-D seismic reflection, vertical seismic profiling (VSP) on a single well, 3-D seismic imaging, and a report of the integrated seismic studies. Recently, Presco Energy conducted an aeromagnetic survey and is currently in the process of applying 2-D VSP methods to target exploration and production wells at the site. These studies have indicated that geothermal fluid flow primarily occurs along faults and fractures and that two potential aquifers include a sandstone/siltstone member of the Triassic Natchez Pass Formation and a karst zone that occurs at the interface between Mesozoic limestone and Tertiary volcanics. We hypothesized that addition of a high-resolution gravity survey would better define the locations, trends, lengths, and dip angles of faults and possible solution cavity features. The gravity survey encompassed an area of approximately 78 km2 (30 mi2) within the boundary of the KGRA along with portions of 8 sections directly to the west and 8 sections directly to the east. The survey included 203 stations that were spaced at 400 m intervals. The simple Bouguer anomaly patterns were coincident with elevation, and those patterns remained after terrain corrections were performed. To remove this signal, the data were further processed using wave-length (bandpass) filtering techniques. The results of the filtering and comparison with the recent aeromagnetic survey indicate that the location and trend of major fault systems can be identified using this technique. Dip angles can be inferred by the anomaly contour gradients. By further reductions in the bandpass window, other features such as possible karst solution channels may also be recognizable. Drilling or other geophysical methods such as a

  3. Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

    USGS Publications Warehouse

    Harmon, N.; Forsyth, D.W.; Scheirer, D.S.

    2006-01-01

    The Gravity Lieations Intraplate Melting Petrologic and Seismic Expedition (GLIMPSE) Experiment investigated the formation of a series of non-hot spot, intraplate volcanic ridges in the South Pacific and their relationship to cross-grain gravity lineaments detected by satellite altimetry. Using shipboard gravity measurements and a simple model of surface loading of a thin elastic plate, we estimate effective elastic thicknesses ranging from ???2 km beneath the Sojourn Ridge to a maximum of 10 km beneath the Southern Cross Seamount. These elastic thicknesses are lower than predicted for the 3-9 Ma seafloor on which the volcanoes lie, perhaps due to reheating and thinning of the plate during emplacement. Anomalously low apparent densities estimated for the Matua and Southern Cross seamounts 2050 and 2250 kg m-3, respectively, probably are artifacts caused by the assumption of only surface loading, ignoring the presence of subsurface loading in the form of underplated crust and/or low-density mantle. Using satellite free-air gravity and shipboard bathymetry, we calculate the age-detrended, residual mantle Bouguer anomaly (rMBA). The rMBA corrects the free-air anomaly for the direct effects of topography, including the thickening of the crust beneath the seamounts and volcanic ridges due to surface loading of the volcanic edifices. There are broad, negative rMBA anomalies along the Sojourn and Brown ridges and the Hotu Matua seamount chain that extend nearly to the East Pacific Rise. These negative rMBA anomalies connect to negative free-air anomalies in the western part of the study area that have been recognized previously as the beginnings of the cross-grain gravity lineaments. Subtracting the topographic effects of surface loading by the ridges and seamounts from the observed topography reveals that the ridges are built on broad bands of anomalously elevated seafloor. This swell topography and the negative rMBA anomalies contradict the predictions of lithospheric

  4. Structure and evolution of the Molucca Sea area: constraints based on interpretation of a combined sea-surface and satellite gravity dataset

    NASA Astrophysics Data System (ADS)

    Widiwijayanti, Christina; Mikhailov, Valentin; Diament, Michel; Deplus, Christine; Louat, Rémy; Tikhotsky, Sergei; Gvishiani, Alexei

    2003-10-01

    The paper presents an interpretation of the complete Bouguer gravity anomaly for the Molucca Sea area (northeast of Indonesia) in order to investigate the structure and interrelation of the main tectonic units of the region. Data on the gravity field and topography incorporate all available shipboard and satellite-derived data, including data collected during a 1994 R/V L'Atalante cruise in the Molucca Sea (MODEC). These data were compiled by weighted interpolation of surface and satellite data. The anomalous gravity field of the area contains components of different wavelengths, which we separated into regional and local anomalies using a spherical analogue of Kolmogorov-Wiener optimal (mean-square) filtering. Position and depth of the shallow lithospheric gravity sources were then estimated from the local field component by applying a new approach to Euler solution selection based on a recently developed fuzzy logic clustering method, called RODIN. The spatial distribution and depth of Euler solutions provide new information on the tectonic structure of the upper lithosphere resulting from the convergence of the Philippine Sea, Eurasian and Australian plates. The local Bouguer anomalies and dense clusters of Euler solutions make it easy to trace the Sangihe Trench further north, up to 5.5°N, joining it to the Pujada and Miangas ridges and to trace the Miangas Ridge southwards to its junction with the Central Ridge. Seismic data revealing compressive structure and dense shallow clusters of Euler solutions suggest that the Pujada Ridge overthrusts the Miangas Ridge from the west. Clusters of Euler solutions also clearly outline an ophiolite body of the Talaud Archipelago, show main thrust zones bounding it, and trace the southern termination of the Philippine Fault horsetail structure up to 5.5-6°N in the area southeast of Mindanao Island. Our results support the hypothesis that the Talaud Archipelago was formed in situ as an uplifted Central Ridge block. We

  5. Gravity and aeromagnetic constraints on the extent of Cenozoic volcanic rocks within the Nefza Tabarka region, northwestern Tunisia

    NASA Astrophysics Data System (ADS)

    Jallouli, Chokri; Mickus, Kevin; Turki, Mohamed Moncef; Rihane, Chedly

    2003-03-01

    Bouguer gravity and aeromagnetic data are analyzed to determine the extent of Miocene magmatism in the Nefza and Tabarka regions of northwestern Tunisia. Construction of magnetic intensity and enhanced analytic signal (EAS) maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the Nefza and Tabarka regions. Because of the lack of lateral resolution of the EAS techniques, 3-D magnetic and 2.5-D gravity models were constructed over the anomalies at Nefza and Tabarka. The final models indicate that the maximum depths of the igneous bodies are between 2.5 and 2.7 km with maximum widths between 15 and 22 km. The final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust (at least 3 km). These widths greatly expand the region of known Miocene magmatism in northwestern Tunisia. Combined with geochemical and petrological data of the surface volcanic rocks, the gravity and magnetic models imply a wider range of Miocene volcanic activity in northern Tunisia, probably related to a subduction zone.

  6. Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

    NASA Astrophysics Data System (ADS)

    Sun, Bin; Wang, Liangshu; Dong, Ping; Wu, YongJing; Li, Changbo; Hu, Bo; Wang, Chong

    2012-11-01

    The Hailar Basin is one of the typical basins among the NE China Basin Groups, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of magnetic, gravity, petrophysical, geothermal and seismological data, we separate the Gravity and Magnetic Anomalies (GMA) into four orders using Wavelet Multi-scale Decomposition (WMD). The apparent depths of causative sources were then assessed by Power Spectrum Analysis (PSA) of each order. Low-order wavelet detail anomalies were used to study the basin's basement structure such as major faults, the basement lithology, uplifts and depressions. High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method. The results show that the Moho uplifting area of the Hailar Basin is located at the NE part of the basin, the Curie uplifting area is at the NW part, and neither of them is consistent with the basin's sedimentary center. This indicates that the Hailar Basin may differ in basin building pattern from other middle and eastern basins of the basin groups, and the Hailar Basin might be of a passive type. When the Pacific Plate was subducting to NE China, the frontier of the plate lying on the mantle transition zone didn't pass through the Great Khingan Mountains region, so there is not an obvious magma upwelling or lithospheric extension in the Hailar Basin area. Finally, based on the seismological data and results of WMD, a probable 2D crust model is derived from an across-basin profile using the 2D forward modeling of the Bouguer gravity anomaly. The results agree with those from seismic inversion, suggesting WMD is suitable for identifying major crustal density interfaces.

  7. A computer system for the storage and retrieval of gravity data, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Godson, Richard H.; Andreasen, Gordon H.

    1974-01-01

    A computer system has been developed for the systematic storage and retrieval of gravity data. All pertinent facts relating to gravity station measurements and computed Bouguer values may be retrieved either by project name or by geographical coordinates. Features of the system include visual display in the form of printer listings of gravity data and printer plots of station locations. The retrieved data format interfaces with the format of GEOPAC, a system of computer programs designed for the analysis of geophysical data.

  8. Investigating subglacial landscapes and crustal structure of the Gamburtsev Province in East Antarctica with the aid of new airborne gravity data

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Studinger, M.; Bell, R. E.; Damaske, D.; Elieff, S.; Finn, C.; Braaten, D. A.; Corr, H.

    2009-12-01

    The AGAP project was undertaken as part of the 2008\\09 field season and explored the Gamburtsev Subglacial Mountains (GSM) province in East Antarctica. AGAP collected >120, 000 line km of new airborne radar, aerogravity and aeromagnetic data. Here we focus on the airborne gravity part of the survey. The airborne gravity data were collected from two Twin Otters operating from remote field camps either side of Dome A. A high-resolution Sander Geophysics AIRGrav system was used for the first time in Antarctica and was mounted in the US plane. A more traditional L&R airborne gravity meter modified by ZLS was installed on the British Antarctic Survey aircraft. The AIRGrav system was flown in draped mode, which proved ideal for the simultaneous acquisition of radar and magnetic data, while the L&R system required flying along constant elevation survey blocks. The processed free-air gravity anomalies exhibit low cross-over errors of 1 mGal over the southern sector of the GSM, where the AIRGrav system was primarily used, and a spatial resolution of 3.5 km. Larger cross-over errors of 3.5 mGal and a coarser spatial resolution of 8 km characterise the northern part of the GSM and the adjacent Lambert Glacier, where the L&R meter was mainly flown. The merged free-air gravity anomaly grid primarily reflects the subglacial topography of the GSM province. The contrast between the Pensacola-Pole and Lambert Glacier basins and the rugged alpine-type relief of the GSM is clearly imaged. A dentritic system of subglacial valleys is mapped in the GSM, in good agreement with independent radar data. Inversion of the free-air gravity data assists in tracing the bedrock under several km-thick and fast-flowing crevassed ice of the Lambert Glacier. Using the ice thickness and bedrock topography data derived from airborne radar we compiled a new Bouguer anomaly map for the GSM province. The new gravity anomaly data can be used to estimate crustal thickness variations under the GSM and

  9. Gravitational Spacecraft Anomalies as well as the at Present Relatively large Uncertainty of Newton's Gravity Constant are Explained on the Basis of Force-Effects Due to a so-far Unknown Form of Space-like Matter

    NASA Astrophysics Data System (ADS)

    Volkamer, Klaus

    2009-09-01

    Recently, a so-far unkown form of invisible, space-like and field-like form of matter was detected with real, weighable mass content. The observed quanta of field-like matter exhibit in laboratory experiments Planck mass mp = ℏ.c/G = 21.77 μg. They show either a positive or negative sign, and can be understood as candidates for dark matter (field-like quanta with positive sign) and dark energy (field-like quanta with negative sign). Due to the observed gravitational as well as ``topological'' (i.e. form-specific at phase borders) interaction of space-like matter, celestial objects at various scales build up quantized fields of these forms of matter around their centers' of gravity of normal matter which reach far beyond the observable surface of such objects, respectively. From the description of he space-like matter fields of the Sun and the Earth a quantitative explanation of the reported NASA spacecraft anomalies of Pioneer 10 and 11 as well as of NEAR-Shoemaker at its fly-by maneuver on 01/23/1998 at Earth is given. The structure of such quantized subtle matter fields of stars allow in addition a description of the formation of ``normal'' and ``inverse'' planetary nebulae at the end of a star's life.-So-far unknown physical force-effects between subtle matter fields, bound, due to the topological interaction, at various metals were observed. The results allow an explanation of the at present relatively large uncertainty ΔG/G in the determination of Newton's constant of gravity. Devices for a more precise and reproducible determination of G (with an accuracy comparable to that of Planck's quantum of action, for example) should be made of beryllium or aluminium/berylUum alloy to eliminate subtle matter effects or such effects should be taken into account by a comprehensive theoretical modeling of their material and shape (and also to some extend time and place) depending force actions. Thus, both anomalies, the reported NASA spacecraft acceleration anomalies

  10. Size and structure of the Chicxulub crater revealed by horizontal gravity gradients and cenotes

    NASA Astrophysics Data System (ADS)

    Hildebrand, A. R.; Pilkington, M.; Connors, M.; Ortiz-Aleman, C.; Chavez, R. E.

    1995-08-01

    IT is now widely believed that a large impact occurred on the Earth at the end of the Cretaceous period, and that the buried Chicxulub structure in Yucatán, Mexico, is the resulting crater24. Knowledge of the size and internal structure of the Chicxulub crater is necessary for quantifying the effects of the impact on the Cretaceous environment. Although much information bearing on the crater's structure is available, diameter estimates range from 170 to 300 km (refs 1á¤-7), corresponding to an order of magnitude variation in impact energy. Here we show the diameter of the crater to be ~180 km by examining the horizontal gradient of the Bouguer gravity anomaly over the structure. This size is confirmed by the distribution of karst features in the Yucatan region (mainly water-filled sinkholes, known as cenotes). The coincidence of cenotes and peripheral gravity-gradient maxima suggests that cenote formation is closely related to the presence of slump faults near the crater rim.

  11. 3D Geothermal Modelling Using Gravity Survey on Dolok Marawa, Simalungun District, North Sumatera

    NASA Astrophysics Data System (ADS)

    Rivandi, A.; Destawan, R.; Fajri, Z. R.; Hidayat, W.

    2016-01-01

    In North Sumatera, gravity method is applied to identify the geothermal model. This method measured the earth gravitational field. This research has 160 measurement points covering 9 square kilometers. We obtained complete Bouguer anomaly values ranging 85 mGal - 130.68 mGal interpreted as a heat source of andesitic igneous rocks that are affected by the presence of Mount Bahtopu magma chamber. We interpreted the values between 40 mGal - 80 mGal as reservoir and caprock. The 3D gravity inverse modelling conducted using Gravblox, and identifying the following lithologies; Toba Pyroclastic Fall (Qjt) with density 1.92 g/cm3, Toba Pyroclastic Flow (Qjt) with density 2.00 g/cm3, Mount Bahtopu Andesite (Qlb) with density 2.4 g/cm3, and 2.6 g/cm3 which is interpreted as heat source in form of andesitic rock and Mount Bahtopu magma chamber. This heat source is estimated to be at a depth of 1.45 km to 3.78 km below the surface.

  12. High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability?

    NASA Astrophysics Data System (ADS)

    Eppelbaum, Lev

    2015-04-01

    the Lesser Caucasus (western Azerbaijan) under conditions of rugged relief and complex geology. This deposit is well investigated by mining and drilling operations and therefore was used as a reference field polygon for testing this approach. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly and the gravity field determined from a 3D model of a uniform medium with a real topography. 3-D terrain relief model with an interval of its description of 80 km (the investigated 6 profiles of 800 m length are in the center of this interval) was employed to compute (by the use of GSFC software (Khesin et al., 1996)) the gravitational effect of the medium (σ = 2670 kg/m3). With applying such a scheme the Bouguer anomalies were obtained with accuracy in two times higher than that of TC received by the conventional methods. As a result, on the basis of the improved Bouguer gravity with the precise TC data, the geological structure of the deposit was defined (Khesin et al., 1996). Second approach Second approach was employed at the complex Katekh pyrite-polymetallic deposit, which is located at the southern slope of the Greater Caucasus (northern Azerbaijan). The main peculiarities of this area are very rugged topography of SW-NE trend, complex geology and severe tectonics. Despite the availability of conventional ΔgB (TC far zones were computed up to 200 km), for the enhanced calculation of surrounding terrain topography a digital terrain relief model was created (Eppelbaum and Khesin, 2004). The SW-NE regional topography trend in the area of the Katekh deposit occurrence was computed as a rectangular digital terrain relief model (DTRM) of 20 km long and 600 m wide (our interpretation profile with a length of 800 m was located in the geometrical center of the DTRM). As a whole

  13. The determination of potential difference by the joint application of measured and synthetical gravity data: a case study in Hungary

    NASA Astrophysics Data System (ADS)

    Papp, Gábor; Szeghy, Erika; Benedek, Judit

    2009-06-01

    In an elementary approach every geometrical height difference between the staff points of a levelling line should have a corresponding average g value for the determination of potential difference in the Earth’s gravity field. In practice this condition requires as many gravity data as the number of staff points if linear variation of g is assumed between them. Because of the expensive fieldwork, the necessary data should be supplied from different sources. This study proposes an alternative solution, which is proved at a test bed located in the Mecsek Mountains, Southwest Hungary, where a detailed gravity survey, as dense as the staff point density (~1 point/34 m), is available along a 4.3-km-long levelling line. In the first part of the paper the effect of point density of gravity data on the accuracy of potential difference is investigated. The average g value is simply derived from two neighbouring g measurements along the levelling line, which are incrementally decimated in the consecutive turns of processing. The results show that the error of the potential difference between the endpoints of the line exceeds 0.1 mm in terms of length unit if the sampling distance is greater than 2 km. Thereafter, a suitable method for the densification of the decimated g measurements is provided. It is based on forward gravity modelling utilising a high-resolution digital terrain model, the normal gravity and the complete Bouguer anomalies. The test shows that the error is only in the order of 10-3mm even if the sampling distance of g measurements is 4 km. As a component of the error sources of levelling, the ambiguity of the levelled height difference which is the Euclidean distance between the inclined equipotential surfaces is also investigated. Although its effect accumulated along the test line is almost zero, it reaches 0.15 mm in a 1-km-long intermediate section of the line.

  14. Effective photons in weakly absorptive dielectric media and the Beer-Lambert-Bouguer law

    NASA Astrophysics Data System (ADS)

    Judge, A. C.; Brownless, J. S.; Bhat, N. A. R.; Sipe, J. E.; Steel, M. J.; de Sterke, C. Martijn

    2014-04-01

    We derive effective photon modes that facilitate an intuitive and convenient picture of photon dynamics in a structured Kramers-Kronig dielectric in the limit of weak absorption. Each mode is associated with a mode field distribution that includes the effects of both material and structural dispersion, and an effective line-width that determines the temporal decay rate of the photon. These results are then applied to obtain an expression for the Beer-Lambert-Bouguer law absorption coefficient for unidirectional propagation in structured media consisting of dispersive, weakly absorptive dielectric materials.

  15. Bouguer images of the North American craton and its structural evolution

    NASA Technical Reports Server (NTRS)

    Arvidson, R. E.; Bowring, S.; Eddy, M.; Guinness, E.; Leff, C.; Bindschadler, D.

    1984-01-01

    Digital image processing techniques have been used to generate Bouguer images of the North American craton that diplay more of the granularity inherent in the data as compared with existing contour maps. A dominant NW-SE linear trend of highs and lows can be seen extending from South Dakota, through Nebraska, and into Missouri. The structural trend cuts across the major Precambrian boundary in Missouri, separating younger granites and rhyolites from older sheared granites and gneisses. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.

  16. Gravity domains and assembly of the North American continent by collisional tectonics

    NASA Technical Reports Server (NTRS)

    Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

    1988-01-01

    A gravity trend map of North America, based on a horizontal Bouguer gravity gradient map produced from gravity data for Canada and the conterminous United States, is presented and used to define a continental mosaic of gravity trend domains akin to structural domains. Contrasting trend characteristics at gravity domain boundaries support the concept of outward growth of the continent primarily by accretionary tectonics. Gravity patterns, however, indicate a different style of tectonics dominated in the development of now-buried Proterozoic orogenic belts in the south-central United States, supporting a view that these belts formed along the leading edge of a southward-migrating Proterozoic continental margin.

  17. Structure of the Hat Creek graben region: Implications for the structure of the Hat Creek graben and transfer of right-lateral shear from the Walker Lane north of Lassen Peak, northern California, from gravity and magnetic anomalies

    USGS Publications Warehouse

    Langenheim, Victoria; Jachens, Robert C.; Clynne, Michael A.; Muffler, L. J. Patrick

    2016-01-01

    Interpretation of magnetic and new gravity data provides constraints on the geometry of the Hat Creek Fault, the amount of right-lateral offset in the area between Mt. Shasta and Lassen Peak, and confirmation of the influence of pre-existing structure on Quaternary faulting. Neogene volcanic rocks coincide with short-wavelength magnetic anomalies of both normal and reversed polarity, whereas a markedly smoother magnetic field occurs over the Klamath Mountains and its Paleogene cover. Although the magnetic field over the Neogene volcanic rocks is complex, the Hat Creek Fault, which is one of the most prominent normal faults in the region and forms the eastern margin of the Hat Creek Valley, is marked by the eastern edge of a north-trending magnetic and gravity high 20-30 km long. Modeling of these anomalies indicates that the fault is a steeply dipping (~75-85°) structure. The spatial relationship of the fault as modeled by the potential-field data, the youngest strand of the fault, and relocated seismicity suggests that deformation continues to step westward across the valley, consistent with a component of right-lateral slip in an extensional environment. Filtered aeromagnetic data highlight a concealed magnetic body of Mesozoic or older age north of Hat Creek Valley. The body’s northwest margin strikes northeast and is linear over a distance of ~40 km. Within the resolution of the aeromagnetic data (1-2 km), we discern no right-lateral offset of this body. Furthermore, Quaternary faults change strike or appear to end, as if to avoid this concealed magnetic body and to pass along its southeast edge, suggesting that pre-existing crustal structure influenced younger faulting, as previously proposed based on gravity data.

  18. Basin-fill Aquifer Modeling with Terrestrial Gravity: Assessing Static Offsets in Bulk Datasets using MATLAB; Case Study of Bridgeport, CA

    NASA Astrophysics Data System (ADS)

    Mlawsky, E. T.; Louie, J. N.; Pohll, G.; Carlson, C. W.; Blakely, R. J.

    2015-12-01

    Understanding the potential availability of water resources in Eastern California aquifers is of critical importance to making water management policy decisions and determining best-use practices for California, as well as for downstream use in Nevada. Hydrologic well log data can provide valuable information on aquifer capacity, but is often proprietarily inaccessible or economically unfeasible to obtain in sufficient quantity. In the case of basin-fill aquifers, it is possible to make estimates of aquifer geometry and volume using geophysical surveys of gravity, constrained by additional geophysical and geological observations. We use terrestrial gravity data to model depth-to-basement about the Bridgeport, CA basin for application in preserving the Walker Lake biome. In constructing the model, we assess several hundred gravity observations, existing and newly collected. We regard these datasets as "bulk," as the data are compiled from multiple sources. Inconsistencies among datasets can result in "static offsets," or artificial bull's-eye contours, within the gradient. Amending suspect offsets requires the attention of the modeler; picking these offsets by hand can be a time-consuming process when modeling large-scale basin features. We develop a MATLAB script for interpolating the residual Bouguer anomaly about the basin using sparse observation points, and leveling offset points with a user-defined sensitivity. The script is also capable of plotting gravity profiles between any two endpoints within the map extent. The resulting anomaly map provides an efficient means of locating and removing static offsets in the data, while also providing a fast visual representation of a bulk dataset. Additionally, we obtain gridded basin gravity models with an open-source alternative to proprietary modeling tools.

  19. Lunar farside gravity - An assessment of satellite to satellite tracking techniques and gravity gradiometry

    NASA Technical Reports Server (NTRS)

    Ananda, M.; Lorell, J.; Flury, W.

    1976-01-01

    The estimation of local gravity anomalies represented by point masses using gravity gradiometer and satellite to satellite tracking data is discussed. A simulation analysis has been performed to study the recovery of local gravity anomalies from both rotating single axis gravity gradiometer and satellite to satellite tracking measurements. A Lunar Polar Orbiter mission concept is adopted for the orbits and data links. The sensitivity of the gravity determination to data noise, mass point spatial distribution (model errors), unmodelled gravity (gravity anomalies outside the area of interest), and orbit errors is studied. Figure of merit for the comparison is the rms error of radial acceleration.

  20. On the link between particle size and deviations from the Beer-Lambert-Bouguer law for direct transmission

    NASA Astrophysics Data System (ADS)

    Larsen, Michael L.; Clark, Aaron S.

    2014-01-01

    Ballistic photon models of radiative transfer in discrete absorbing random media have demonstrated deviations from the Beer-Lambert-Bouguer law of exponential attenuation. A number of theoretical constructs to quantify the deviation from the Beer-Lambert-Bouguer law have appeared in the literature, several of which rely principally on a statistical measure related to the statistics of the absorber spatial positions alone. Here, we utilize a simple computational model to explore the interplay between the geometric size of the absorbing obstacles and the statistics governing the placement of the absorbers in the volume. We find that a description of the volume that depends on particle size and the spatial statistics of absorbers is not sufficient to fully characterize deviations from the Beer-Lambert-Bouguer law. Implications for future further theoretical and computational explorations of the problem are explored.

  1. Crustal structure in the vicinity of Las Vegas, Nevada, from seismic and gravity observations

    USGS Publications Warehouse

    Roller, John C.

    1963-01-01

    A seismic-refraction profile indicates that the crust of the Earth increases in thickness by as much as 5 km over a horizontal distance of less than 25 km northeast of Las Vegas, Nevada. This feature correlates with a decrease in the Bouguer anomaly and an increase in the average surface altitude.

  2. Evidence of partial melting beneath the passive margin of the Gulf of Aden from a joint analysis of gravity and seismology

    NASA Astrophysics Data System (ADS)

    Basuyau, C.; Tiberi, C.; Leroy, S.; Ebinger, C.; Al-Lazki, A.; Al-Tobi, K.

    2007-12-01

    Rifting processes though extensively studied are still not well known. Nevertheless geophysical studies can provide new insight into the mechanisms of continental opening. The Gulf of Aden is a young narrow and obliquely opening oceanic basin formed during the Olig-Miocene. Its conjugate margins are well preserved beneath a thin post-rift sedimentary cover.It thus makes it an ideal region to study the processes of rifting and continental lithospheric break-up. In 2003 and 2005, numerous teleseismic earthquakes were recorded at twenty-nine broadband seismic stations in Dhofar (Oman) in order to study the northern margin of the Gulf of Aden. In this work, we used a joint inversion of teleseismic P-wave delay times and Bouguer anomaly. We obtain velocity ans density models that shows (1) crustal heterogeneities that match to the main geological features at the surface, (2) the presence of two low velocity anomalies in the continuation of Socotra and Alula Fartak fracture zones that appear at 60 km depth and may extend to at least 200 km, (3) gravity edge effect on the margin. The S wave tomography results are consistent with the joint inversion ones, and evidence partial melting within the two deep velocity anomalies. These results which suggest that the Afar hotspot has an influence up to the Dhofar will be discussed.

  3. Up-to-date Terrain Correction Evaluation within the Gravity Database of the Slovak Republic

    NASA Astrophysics Data System (ADS)

    Pasteka, R.; Zahorec, P.; Marusiak, I.; Mikuška, J.; Papčo, J.; Bielik, M.

    2014-12-01

    In our contribution we present a new method for the evaluation of terrain corrections (TC) and/or topographical effects (TE) for the Gravity Database of the Slovak Republic - using a new software solution (program Toposk) and up to date high-quality digital terrain models. The program was successfully tested on several synthetic models. In our algorithm we have used the well established approach, developed by the gravimetrical school in former Czechoslovakia i.e. dividing the surrounding area into so called inner zone T1 (0 - 250 m), intermediate zone T2 (250 - 5240 m) and outer zone (5.24 - 166.7 km). When calculating the T1 zone contribution we have used interpolated station elevations instead the measured ones, which yield in our opinion better solution to the problem of small-scale inaccuracies of the detailed terrain model. Newly recalculated TC values for the Gravity Database of the Slovak Republic (total number of gravity stations equals 212478, with an average of 3-6 points/km2) are in the range from 0.20 to 79.84 mGal (for the correction density 2.67 gcm-3). Thanks to the new TC values, the final version of the obtained Bouguer anomaly field is more independent from non-geological influences and determines in a better way the information content on the lithospheric density distributions.In the frame of the presented recalculation of regional gravity database we have worked with the concept of terrain corrections, but for other types of gravity method applications, the evaluation of topographical effects is much more straightforward - e.g. elimination of the effect of topography in the vertical gravity (tower) gradients approximation or during processing of absolute gravity measurements (with FG-5 and/or A-10 gravity meters). Another very important property of our proposed approach is that we can evaluate TC and TE in calculating points below the Earth's surface (applicable also in borehole gravity method, BHGM). This work was supported by the Slovak

  4. Aeromagnetic, gravity anomaly, and derivative maps of the Craig and Dixon Entrance 1-degree by 3-degree quadrangles of southeastern Alaska

    USGS Publications Warehouse

    Wynn, Jeffrey C.; Kucks, R.P.; Grybeck, D.J.

    1999-01-01

    This CD-ROM contains aeromagnetic, gravity, geology, and topographic data as well as several derivative products, for the Craig and Dixon Entrance 1? ? 3? quadrangles of Southeastern Alaska. The data were collected by the U.S. Geological Survey directly and by means of several contract airborne surveys, through August 1991.

  5. Mass Anomalies on Ganymede

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Anderson, J. D.; Jacobson, R. A.; Lau, E. L.; Moore, W. B.; Palguta, J.

    2004-01-01

    Radio Doppler data from two Ganymede encounters (G1 and G2) on the first two orbits in the Galileo mission have been analyzed previously for gravity information . For a satellite in hydrostatic equilibrium, its gravitational field can be modeled adequately by a truncated spherical harmonic series of degree two. However, a fourth degree field is required in order to fit the second Galileo flyby (G2). This need for a higher degree field strongly suggests that Ganymede s gravitational field is perturbed by a gravity anomaly near the G2 closest approach point (79.29 latitude, 123.68 west longitude). In fact, a plot of the Doppler residuals , after removal of the best-fit model for the zero degree term (GM) and the second degree moments (J2 and C22), suggests that if an anomaly exists, it is located downtrack of the closest approach point, closer to the equator.

  6. World gravity standards

    NASA Technical Reports Server (NTRS)

    Uotila, U. A.

    1978-01-01

    In order to use gravity anomalies in geodetic computations and geophysical interpretations, the observed gravity values from which anomalies are derived should be referred to one consistent world wide system. The International Gravity Standardization Net 1971 was adapted by the International Union of Geodesy and Geophysics at Moscow in 1971, the network was result of extensive cooperation by many organizations and individuals around the world. The network contains more than 1800 stations around the world. The data used in the adjustment included more than 25,000 gravimetry, pendulum and absolute measurements.

  7. Depth distribution of the sedimentary basin and Moho undulation in the Yellow Sea, NE Asia interpreted by using satellite-derived gravity field

    NASA Astrophysics Data System (ADS)

    Choi, Sungchan; Ryu, In-Chang; Götze, H.-J.

    2015-07-01

    We interpreted the TRIDENT satellite derived gravity field to provide detailed insights into the spatial distribution of the crustal density structures in the area of the Yellow Sea. We used 3-D forward density modelling for the interpretation that incorporated constraints from existing geological and geophysical information. A gravity stripping method is used to separate out the gravity effects of different geological crustal structures. From this analysis we see that (1) the Gunsan sedimentary basin is isostatically compensated. (2) The satellite-derived Bouguer anomalies ranging from 15 to -30 × 10-5 m s-2 are linked to basin thicknesses in the Yellow Sea. (3) The calculated Moho depth in the Yellow Sea varies from 27 km beneath the deep sedimentary basin to 34 km in the uplifted zones. (4) Moho depth calculations show two distinct areas, characterized by the deepest Moho depths and the largest crustal thicknesses in the Yellow Sea. The one region extends along the Qianliyan Uplift Zone from Jiaodong to Hongsung while the other area extends from southeastern China to Hongsung in the Korean peninsula. Compared to previous works we suggest that they are the part of the collisions zone between North and South China Blocks extending from China to the Korean peninsula via the Yellow Sea.

  8. On isostatic geoid anomalies

    NASA Technical Reports Server (NTRS)

    Haxby, W. F.; Turcotte, D. L.

    1978-01-01

    In regions of slowly varying lateral density changes, the gravity and geoid anomalies may be expressed as power series expansions in topography. Geoid anomalies in isostatically compensated regions can be directly related to the local dipole moment of the density-depth distribution. This relationship is used to obtain theoretical geoid anomalies for different models of isostatic compensation. The classical Pratt and Airy models give geoid height-elevation relationships differing in functional form but predicting geoid anomalies of comparable magnitude. The thermal cooling model explaining ocean floor subsidence away from mid-ocean ridges predicts a linear age-geoid height relationship of 0.16 m/m.y. Geos 3 altimetry profiles were examined to test these theoretical relationships. A profile over the mid-Atlantic ridge is closely matched by the geoid curve derived from the thermal cooling model. The observed geoid anomaly over the Atlantic margin of North America can be explained by Airy compensation. The relation between geoid anomaly and bathymetry across the Bermuda Swell is consistent with Pratt compensation with a 100-km depth of compensation.

  9. Three-dimensional crustal structure of the southern Sierra Nevada from seismic fan profiles and gravity modeling

    SciTech Connect

    Fliedner, M.M.; Ruppert, S.; Park, S.K.; and others.

    1996-04-01

    Traveltime data from the 1993 Southern Sierra Nevada Continental Dynamics seismic refraction experiment reveal low velocities in the southern Sierra Nevada and Basin and Range province of California (6.0 to 6.6 km/s), as well as low upper mantle velocities (7.6 to 7.8 km/s). The crust thickens from southeast to northwest along the axis of the Sierra Nevada from 27 km in the Mojave Desert to 43 km near Fresno, California. A crustal welt is present beneath the Sierra Nevada, but the deepest Moho is found under the western slopes, not beneath the highest topography. A density model directly derived from the crustal velocity model but with constant mantle density satisfies the pronounced negative Bouguer anomaly associated with the Sierra Nevada, but shows large discrepancies of >50 mgal in the Great Valley and in the Basin and Range province. Matching the observed gravity with anomalies in the crust alone is not possible with geologically reasonable densities; we require a contribution from the upper mantle, either by lateral density variations or by a thinning of the lithosphere under the Sierra Nevada and the Basin and Range province. Such a model is consistent with the interpretation that the uplift of the present Sierra Nevada is caused and dynamically supported by asthenospheric upwelling or lithospheric thinning under the Basin and Range province and eastern Sierra Nevada. 20 refs., 4 figs.

  10. Satellite elevation magnetic anomaly maps

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J. (Principal Investigator)

    1982-01-01

    The problem of inverting 2 deg average MAGSAT scalar anomalies for the region 80 W, 60 E longitude and 40 S, 70 N latitude was attempted on the LARS computer; however, the effort was aborted due to insufficient allocation of CPU-time. This problem is currently being resubmitted and should be implemented shortly for quantitative comparison with free-air gravity anomaly, geothermal, and tectonic data.

  11. FORTRAN program for automatic terrain correction of gravity measurements

    NASA Astrophysics Data System (ADS)

    Ballina Lopez, Hugo Rainier

    The use of a digital computer in the calculation of the Bouguer anomaly terrain correction vastly simplifies the process and reduces the manhours required by up to 80%. The FORTRAN language program presented here was written for a UNIVAC 1100/90 computer (the program works in any type of computer that has a FORTRAN compiler) and successfully applied in a geothermal zone in Jalisco State, Mexico, where it used a 103 × 82 km matrix.

  12. Gravity data of the Norcia and Castelluccio basins (central Italy): insight for active faulting of the area

    NASA Astrophysics Data System (ADS)

    Ruano, P.; Rustichelli, A.; Galindo-Zaldívar, J.; Piccardi, L.; Ruiz-Constán, A.; Tondi, E.; López-Garrido, A. C.; Sanz de Galdeano, C.

    2009-04-01

    The Norcia and Castelluccio basins are located in the central Apennines, the southeastern extension of the NE-vergent arcuate, Neogene, foreland fold and thrust belt of northern Italy. These intramontane depressions are infilled by Pleistocene-Holocene coarse continental fluvial and alluvial deposits, whereas the bedrock units are represented by limestone and pelagic marls of Jurassic to Miocene age. Several historical and instrumental highly destructive earthquakes have occurred in this area: January 14, 1703 (X MCS, M=6.6); September 19, 1979 (Ms= 5.9, focal depth of 6-8km). Fault data and earthquake focal mechanisms show a predominant NE-SW extension, but strike-slip and even reverse mechanisms have also been determined. The surface of the Norcia basin is flat, slightly inclined to the NW, with only an almost isolated basement hill in the middle. The basin has a predominant NNW-SSE elongation with very straight boundaries constituted by oblique-extensional faults. In addition, Castelluccio Depression is a hanging basin located eastwards of the Norcia area. In order to determine the distribution of the sedimentary infill, a gravity survey has been developed in the region, including several profiles orthogonal to the basin edges and additional scattered data that improve the map coverage. Measurements have been done in the basins and also in the basement in order to determine the regional anomalies. A Scintrex CG-5 gravitimeter with an accuracy of 0.001mGal, a barometric altimeter of 0.5 m of precision, and a Garmin e-trex GPS have been used during the acquisition of the 294 measurements. A density of 2.60 g/cm3 (mean density of the basement limestone) has been considered for calculating the Bouguer Anomalies. Terrain corrections have been determined using the SRTM90-m. The Foligno absolute gravity base station has been taking into account during this survey. The Bouguer Anomaly is negative in all the area, with a regional trend that decreases northeastwards

  13. Ocean gravity and geoid determination

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.; Siry, J. W.; Brown, R. D.; Wells, W. T.

    1977-01-01

    Gravity anomalies have been recovered in the North Atlantic and the Indian Ocean regions. Comparisons of 63 2 deg x 2 deg mean free air gravity anomalies recovered in the North Atlantic area and 24 5 deg x 5 deg mean free air gravity anomalies in the Indian Ocean area with surface gravimetric measurements have shown agreement to + or - 8 mgals for both solutions. Geoids derived from the altimeter solutions are consistent with altimetric sea surface height data to within the precision of the data, about + or - 2 meters.

  14. A new 3D Moho depth model for Iran based on the terrestrial gravity data and EGM2008 model

    NASA Astrophysics Data System (ADS)

    Kiamehr, R.; Gómez-Ortiz, D.

    2009-04-01

    Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations and seismologic applications. Dehghani in 1984 estimated the first Moho depth model over the Iranian plateau using the simple profiling method and Bouguer gravity data. However, these data are high deficiencies and lack of coverage in most part of the region. To provide a basis for an accurate analysis of the region's lithospheric stresses, we develop an up to date three dimensional crustal thickness model of the Iranian Plateau using Parker-Oldenburg iterative method. This method is based on a relationship between the Fourier transform of the gravity anomaly and the sum of the Fourier transform of the interface topography. The new model is based on the new and most complete gravity database of Iran which is produced by Kiamehr for computation of the high resolution geoid model for Iran. Total number of 26125 gravity data were collected from different sources and used for generation an outlier-free 2x2 minutes gravity database for Iran. At the mean time, the Earth Gravitational Model (EGM2008) up to degree 2160 has been developed and published by National Geospatial Intelligence Agency. EGM2008 incorporates improved 5x5 minutes gravity anomalies and has benefited from the latest GRACE based satellite solutions. The major benefit of the EGM2008 is its ability to provide precise and uniform gravity data with global data coverage. Two different Moho depth models have been computed based on the terrestrial and EGM2008 datasets. The minimum and maximum Moho depths for land and EGM2008 models are 10.85-53.86 and 15.41-51.43 km, respectively. In general, we found a good agreement between the Moho geometry obtained using both land and EGM2008 datasets with the RMS of 2.7 km. Also, we had a comparison between these gravimetric Moho models versus global seismic crustal models CRUST 2.0. The differences between EGM2008 and land

  15. Holonomy anomalies

    SciTech Connect

    Bagger, J.; Nemeschansky, D.; Yankielowicz, S.

    1985-05-01

    A new type of anomaly is discussed that afflicts certain non-linear sigma models with fermions. This anomaly is similar to the ordinary gauge and gravitational anomalies since it reflects a topological obstruction to the reparametrization invariance of the quantum effective action. Nonlinear sigma models are constructed based on homogeneous spaces G/H. Anomalies arising when the fermions are chiral are shown to be cancelled sometimes by Chern-Simons terms. Nonlinear sigma models are considered based on general Riemannian manifolds. 9 refs. (LEW)

  16. Reliability of CHAMP Anomaly Continuations

    NASA Technical Reports Server (NTRS)

    vonFrese, Ralph R. B.; Kim, Hyung Rae; Taylor, Patrick T.; Asgharzadeh, Mohammad F.

    2003-01-01

    CHAMP is recording state-of-the-art magnetic and gravity field observations at altitudes ranging over roughly 300 - 550 km. However, anomaly continuation is severely limited by the non-uniqueness of the process and satellite anomaly errors. Indeed, our numerical anomaly simulations from satellite to airborne altitudes show that effective downward continuations of the CHAMP data are restricted to within approximately 50 km of the observation altitudes while upward continuations can be effective over a somewhat larger altitude range. The great unreliability of downward continuation requires that the satellite geopotential observations must be analyzed at satellite altitudes if the anomaly details are to be exploited most fully. Given current anomaly error levels, joint inversion of satellite and near- surface anomalies is the best approach for implementing satellite geopotential observations for subsurface studies. We demonstrate the power of this approach using a crustal model constrained by joint inversions of near-surface and satellite magnetic and gravity observations for Maude Rise, Antarctica, in the southwestern Indian Ocean. Our modeling suggests that the dominant satellite altitude magnetic anomalies are produced by crustal thickness variations and remanent magnetization of the normal polarity Cretaceous Quiet Zone.

  17. Gravity survey and regional geology of the Prince William Sound epicentral region, Alaska: Chapter C in The Alaska earthquake, March 27, 1964: regional effects

    USGS Publications Warehouse

    Case, J.E.; Barnes, D.F.; Plafker, George; Robbins, S.L.

    1966-01-01

    Sedimentary and volcanic rocks of Mesozoic and early Tertiary age form a roughly arcuate pattern in and around Prince William Sound, the epicentral region of the Alaska earthquake of 1964. These rocks include the Valdez Group, a predominantly slate and graywacke sequence of Jurassic and Cretaceous age, and the Orca Group, a younger sequence of early Tertiary age. The Orca consists of a lower unit of dense-average 2.87 g per cm3 (grams per cubic centimeter) pillow basalt and greenstone intercalated with sedimentary rocks and an upper unit of lithologically variable sandstone interbedded with siltstone or argillite. Densities of the clastic rocks in both the Valdez and Orca Groups average about 2.69 g per cm3. Granitic rocks of relatively low density (2.62 g per cm3) cut the Valdez and Orca Groups at several localities. Both the Valdez and the Orca Groups were complexly folded and extensively faulted during at least three major episodes of deformation: an early period of Cretaceous or early Tertiary orogeny, a second orogeny that probably culminated in late Eocene or early Oligocene time and was accompanied or closely followed by emplacement of granitic batholiths, and a third episode of deformation that began in late Cenozoic time and continued intermittently to the present. About 500 gravity stations were established in the Prince William Sound region in conjunction with postearthquake geologic investigations. Simple Bouguer anomaly contours trend approximately parallel to the arcuate geologic structure around the sound. Bouguer anomalies decrease northward from +40 mgal (milligals) at the southwestern end of Montague Island to -70 mgal at College and Harriman Fiords. Most of this change may be interpreted as a regional gradient caused by thickening of the continental crust. Superimposed on the gradient is a prominent gravity high of as much as 65 mgal that extends from Elrington Island on the southwest, across Knight and Glacier Islands to the Ellamar Peninsula

  18. Bangui Anomaly

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.

    2004-01-01

    Bangui anomaly is the name given to one of the Earth s largest crustal magnetic anomalies and the largest over the African continent. It covers two-thirds of the Central African Republic and therefore the name derives from the capitol city-Bangui that is also near the center of this feature. From surface magnetic survey data Godivier and Le Donche (1962) were the first to describe this anomaly. Subsequently high-altitude world magnetic surveying by the U.S. Naval Oceanographic Office (Project Magnet) recorded a greater than 1000 nT dipolar, peak-to-trough anomaly with the major portion being negative (figure 1). Satellite observations (Cosmos 49) were first reported in 1964, these revealed a 40nT anomaly at 350 km altitude. Subsequently the higher altitude (417-499km) POGO (Polar Orbiting Geomagnetic Observatory) satellite data recorded peak-to-trough anomalies of 20 nT these data were added to Cosmos 49 measurements by Regan et al. (1975) for a regional satellite altitude map. In October 1979, with the launch of Magsat, a satellite designed to measure crustal magnetic anomalies, a more uniform satellite altitude magnetic map was obtained. These data, computed at 375 km altitude recorded a -22 nT anomaly (figure 2). This elliptically shaped anomaly is approximately 760 by 1000 km and is centered at 6%, 18%. The Bangui anomaly is composed of three segments; there are two positive anomalies lobes north and south of a large central negative field. This displays the classic pattern of a magnetic anomalous body being magnetized by induction in a zero inclination field. This is not surprising since the magnetic equator passes near the center of this body.

  19. Geophysical Investigation of Australian-Antarctic Ridge Using High-Resolution Gravity and Bathymetry

    NASA Astrophysics Data System (ADS)

    Kim, S. S.; Lin, J.; Park, S. H.; Choi, H.

    2015-12-01

    Much of the Australian-Antarctic Ridge (AAR) has been remained uncharted until 2011 because of its remoteness and harsh weather conditions. From 2011, the multidisciplinary ridge program initiated by the Korea Polar Research Institute (KOPRI) surveyed the little-explored eastern ends of the AAR to characterize the tectonics, geochemistry, and hydrothermal activity of this intermediate spreading system. In this study, we present a detailed analysis of a 300-km-long supersegment of the AAR to quantify the spatial variations in ridge morphology and axial and off-axis volcanisms as constrained by high-resolution shipboard bathymetry and gravity. The ridge axis morphology alternates between rift valleys and axial highs within relatively short ridge segments. To obtain a geological proxy for regional variations in magma supply, we calculated residual mantle Bouguer gravity anomalies (RMBA), gravity-derived crustal thickness, and residual topography for neighboring seven sub-segments. The results of the analyses revealed that the southern flank of the AAR is associated with shallower seafloor, more negative RMBA, thicker crust, and/or less dense mantle in comparison to the conjugate northern flank. Furthermore, this north-south asymmetry becomes more prominent toward the KR1 supersegment of the AAR. The axial topography of the KR1 supersegment exhibits a sharp transition from axial highs at the western end to rift valleys at the eastern end, with regions of axial highs being associated with more robust magma supply as indicated by more negative RMBA. We also compare and contrast the characteristics of the AAR supersegment with that of other ridges of intermediate spreading rates, including the Juan de Fuca Ridge, Galápagos Spreading Center, and Southeast Indian Ridge west of the Australian-Antarctic Discordance, to investigate the influence of ridge-hotspot interaction on ridge magma supply and tectonics.

  20. Gravity Fields of the Moon Derived from GRAIL Primary and Extended Mission Data (Invited)

    NASA Astrophysics Data System (ADS)

    Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Loomis, B.; Chinn, D. S.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2013-12-01

    The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft conducted the mapping of the gravity field of the Moon from March 1, 2012 to May 29, 2012, for the primary mission and from August 30, 2012 to December 14, 2012 for the extended mission and endgame. During both mission phases, the twin spacecraft acquired highly precise Ka-band range-rate (KBRR) intersatellite ranging data and Deep Space Network (DSN) data from altitudes of 2.3 to 98.2 km above the lunar surface. We have processed the GRAIL data using the NASA GSFC GEODYN orbit determination and geodetic parameter estimation program and used the supercomputers of the NASA Center for Climate Simulation (NCCS) at NASA GSFC to accumulate the SRIF arrays and derive the geopotential solutions. During the extended mission, the spacecraft orbits were maintained at a mean altitude of ~23 km, compared to ~50 km during the primary mission. In addition, from December 7 to December 14, 2012, data were acquired from a mean altitude of 11.5 km. With these data, we have derived solutions in spherical harmonics to degree 900. The new gravity solutions show improved correlations with LOLA-derived topography to very high degree and order and resolve many lunar features in the geopotential with a resolution of less than 15 km. We discuss the methods we used for the processing of the GRAIL data, and evaluate these solutions with respect to the derived power spectra, Bouguer anomalies, and fits with independent data (such as from the low-altitude phase of the Lunar Prospector mission).

  1. High-resolution Gravity Field Models of the Moon Using GRAIL mission Data

    NASA Astrophysics Data System (ADS)

    Lemoine, Frank G.; Goossens, Sander; Sabaka, Terrence J.; Nicholas, Joseph B.; Mazarico, Erwan; Rowlands, David D.; Loomis, Bryant D.; Chinn, Douglas S.; Neumann, Gregory A.; Smith, David E.; Zuber, Maria T.

    2015-04-01

    The Gravity Recovery and Interior Laboratory (GRAIL) mission was designed to map the structure of the lunar interior from crust to core and to advance the understanding of the Moon's thermal evolution by producing a high-quality, high-resolution map of the gravitational field of the Moon. GRAIL consisted of two spacecraft, with Ka-band tracking between the two satellites as the single science instrument, with the addition of Earth-based tracking using the Deep Space Network. The science mission was divided into two phases: a primary mission from March 1, 2012 to May 29, 2012, and an extended mission from August 30, 2012 to December 14, 2012. The altitude varied from 3 km to 94 km above the lunar surface during both mission phases. Both the primary and the extended mission data have been processed into global models of the lunar gravity field at NASA/GSFC using the GEODYN software up to 1080 x 1080 in spherical harmonics. In addition to the high-resolution global models, local models have also been developed. Due to varying spacecraft altitude and ground track spacing, the actual resolution of the global models varies geographically. Information beyond the current resolution is still present in the data, as indicated by relatively higher fits in the last part of the extended mission, where the satellites achieved their lowest altitude above lunar surface. Local models of the lunar gravitational field at high resolution were thus estimated to accommodate this signal. Here, we present the current status of GRAIL gravity modeling at NASA/GSFC, for both global and local models. We discuss the methods we used for the processing of the GRAIL data, and evaluate these solutions with respect to the derived power spectra, Bouguer anomalies, and fits with independent data (such as from the low-altitude phase of the Lunar Prospector mission). We also evaluate the prospects for extending the resolution of our current models

  2. Relationship between surface and subsurface structures of the northern Atlas foreland of Tunisia deduced from regional gravity analysis

    NASA Astrophysics Data System (ADS)

    Frifita, N.; Arfaoui, M. S.; Zargouni, F.

    2016-08-01

    Gravity data were analyzed in the northern Atlas of Tunisia in order to identify the deep structures of the region and their relationship to the geological outcrop. The analysis based on the Bouguer gravity maps related to upward continuation at 1, 2, 4, 6, 10 and 12 km. The lineaments obtained by the horizontal gradient method were interpreted as deep faults with two global directions NE–SW and NW–SE related to major tectonic corridors. These lineaments were confirmed by the automatic estimation of depth solutions using the Euler deconvolution technique. By separation between the gravity anomaly bodies in different levels, it shows that almost all of the lineaments are oriented in NE–SW and NW–SE directions. The NW–SE-trending lineaments are related to deep faults and the NE–SW-oriented lineaments define the global direction of the surface, and they are related to shallow structures. 2.5D gravity modeling was used to improve the results obtained by the Maxima and the Euler deconvolution techniques. The 2.5D model points out the variation of depths of the NE–SW-trending major faults. In this study, we demonstrate the relationship between the NE–SW and the NW–SE directions. These two major sets of faults have been determined by the statistical study of the lineaments. This study confirms some faults already recognized or supposed by the classical geological studies, and it also detects a new deep fault masked in the surface, and gives information about major fault depths and the relation between different structures.

  3. Gravity study of the Central African Rift system: a model of continental disruption 2. The Darfur domal uplift and associated Cainozoic volcanism

    NASA Astrophysics Data System (ADS)

    Bermingham, P. M.; Fairhead, J. D.; Stuart, G. W.

    1983-05-01

    Gravity studies of the Darfur uplift, Western Sudan, show it to be associated with a circular negative Bouguer anomaly, 50 mGal in amplitude and 700 km across. A three-dimensional model interpretation of the Darfur anomaly, using constraints deduced from geophysical studies of similar but more evolved Kenya and Ethiopia domes, suggests either a low-density laccolithic body at mid-lithospheric depth (~ 60 km) or a thinned lithosphere with emplacement at high level of low-density asthenospheric material. The regional setting of the Darfur uplift is described in terms of it being an integral part of the Central African Rift System which is shown to be broadly equivalent to the early to middle Miocene stage in the development of the Afro-Arabian Rift System. Comparisons between these rift systems suggest that extensional tectonics and passive rifting, resulting in the subsiding sedimentary rift basins associated with the Ngaoundere, Abu Gabra, Red Sea and Gulf of Aden rifts, are more typical of the early stage development of passive continental margins than the active domal uplift and development of rifted features associated with the Darfur, Kenya and Ethiopia domes.

  4. Point stability at shallow depths: experience from tilt measurements in the Lower Rhine Embayment, Germany, and implications for high-resolution GPS and gravity recordings

    NASA Astrophysics Data System (ADS)

    Kümpel, H.-J.; Lehmann, K.; Fabian, M.; Mentes, Gy.

    2001-09-01

    From 1996 to 1999, we have studied ground tilts at depths of between 2m and 5m at three sites in the Lower Rhine Embayment (LRE), western Germany. The LRE is a tectonically active extensional sedimentary basin roughly 50km×100km. The purpose of the tilt measurements was (a) to provide insight into the magnitude, nature and variability of background tilts and (b) to assess possible limitations of high-resolution GPS campaigns and microgravity surveys due to natural ground deformation. The tilt readings, sensed by biaxial borehole tiltmeters of baselength 0.85m, cover a frequency range from 10-8Hz to 10-2Hz (periods from minutes to years). Assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters' baselength, and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity, we try to estimate the magnitude level of point movements and corresponding Bouguer gravity effects that is generally not surpassed. The largest tilt signals observed were some +/-50µradyr-1. If they were observable over a ground section of extension, e.g. 10m, the converted rates may correspond to about +/-0.5mm per 10myr-1 in vertical ground displacement, and +/-0.1µgalyr-1 in Bouguer gravity effect, respectively. Large signals are mostly related to seasonal effects, probably linked to thermomechanical strain. Other causes of ground deformation identified include seepage effects after rainfalls (order of +/-10µrad) and diurnal strains due to thermal heating and/or fluctuations in the water consumption of nearby trees (order of +/-1µrad). Episodic step-like tilt anomalies with amplitudes up to 22µrad at one of the observation sites might reflect creep events associated to a nearby active fault. Except for short-term ground deformation caused by the passage of seismic waves from distant earthquakes, amplitudes of non-identified tilt signals in the studied

  5. Marine gravity image available

    NASA Astrophysics Data System (ADS)

    The image below shows the gravity field from 30-72°S computed from Geosat geodetic mission (GM) and exact repeat mission (ERM) data. A color shaded-relief image of these gravity anomalies is available from NOAA in poster form (report MGG-8, [Marks et al., 1993] and also as a digital gridded data set on CD-ROM. To order, contact the National Geophysical Data Center, E/GC3, 325 Broadway, Boulder, CO 80303.

  6. Gradients from GOCE reveal gravity changes before Pisagua Mw = 8.2 and Iquique Mw = 7.7 large megathrust earthquakes

    NASA Astrophysics Data System (ADS)

    Álvarez, Orlando; Nacif, Silvina; Spagnotto, Silvana; Folguera, Andres; Gimenez, Mario; Chlieh, Mohamed; Braitenberg, Carla

    2015-12-01

    Considerable improvements in the measurement of the Earth gravity field from GOCE satellite mission have provided global gravity field models with homogeneous coverage, high precision and good spatial resolution. In particular, the vertical gravity gradient (Tzz), in comparison to the classic Bouguer anomaly, defines more accurately superficial mass heterogeneities. Moreover, the correction of these satellite-derived data from the effect of Earth topographic masses by means of new techniques taking into account the Earth curvature, improves results in regional analyses. In a recent work we found a correlation between Tzz and slip distribution for the 2010 Maule Mw = 8.8 earthquake. In the present work, we derive the vertical gravity gradient from the last GOCE only model, corrected by the topographic effect and also by the sediments on depocenters of the offshore region at the Peru-Chile margin, in order to study a spatial relationship between different lobes of the gravity derived signal and the seismic sources of large megathrust earthquakes. In particular, we analyze this relation for the slip models of the 1996 Mw = 7.7 Nazca, 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco events and for the slip models of the 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes from Schurr et al. (2014), including the previously analyzed 2010 Mw = 8.8 Maule event. Then we find a good correlation between vertical gravity gradients and main rupture zones, correlation that becomes even stronger as the event magnitude increases. Besides this, a gravity fall in the gravity gradient was noticed over the area of the main slip patches at least for the two years before 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes. Additionally, we found temporal variations of the gravity field after 2010 Mw = 8.8 Maule event, related to the main patches of the slip distribution, and coseismic deformation. Therefore, we analyzed vertical gravity gradient field variations as an indirect measure

  7. Crustal Accretion and Mantle Geodynamics at Microplates: Constraints from Gravity Analysis

    NASA Astrophysics Data System (ADS)

    Ames, K.; Georgen, J. E.; Dordevic, M. M.

    2013-12-01

    Oceanic crustal accretion occurs in a variety of locations, including mid-ocean ridges and back-arc spreading centers, and in unique settings within these systems, such as plate boundary triple junctions, intra-transform spreading centers, and microplates. This study focuses on crustal accretion and mantle geodynamics at microplates. The Easter and Juan Fernandez microplates are located in the South Pacific along the Pacific, Nazca and Antarctic plate boundaries. Both microplates formed 3-5 Ma and they are currently rotating clockwise at 15 deg/Ma and 9 deg/Ma respectively (e.g., Searle et al. J. Geol. Soc. Lond. 1993). The study area also encompasses the Easter/Sala y Gomez mantle plume and the Foundation seamount chain, both of which are located close to spreading centers. We calculate mantle Bouguer anomaly (MBA) from satellite gravity measurements and shipboard soundings in order to gain a better understanding of the thermal structure of these two oceanic microplates and to quantify the effect that melting anomalies may have on their boundaries. We assume a crustal thickness of 6.0 km, a 1.7 g/cm^3 density difference at the water/crust interface, and a 0.6 g/cm^3 density difference at the crust/mantle interface. The west rift of the Easter microplate has an MBA low ranging from approximately -50 to -100 mGal, while the east rift has slightly higher MBA values ranging from roughly 10 to -50 mGal. The west rift of the Juan Fernandez microplate has a maximum MBA low of about -100 mGal with a sharp increase to -20 mGal at -35 deg S. The east rift of the Juan Fernandez microplate is characterized by more variable MBA, ranging from 0 to -140 mGal. The MBA low associated with the Easter/Sala y Gomez mantle plume has a maximum amplitude about 150 mGal. Likewise, the Foundation seamounts show a gravity low of -140 to -150 mGal. These spatial variations in gravity, as well as published isotopic data and exploratory numerical models, are used to constrain upper mantle

  8. Joint inversion of teleseismic and gravity data beneath the Fennoscandian Shield

    NASA Astrophysics Data System (ADS)

    Beller, Stephen; Kozlovskaya, Elena; Achauer, Ulrich; Tiberi, Christel

    2013-04-01

    Many geophysical studies have been performed to understand lithospheric structures and to unravel the evolution and stabilisation of the Fennoscandian Shield, the oldest part (2.5-3.4 Ga) of the East European Craton. However, getting a clear vision of the upper-mantle structure still remains difficult due to a loss of resolution and a poor consistency between different methods. Recently, a huge effort has been made to better constrain regional tomographic inversion using additional informations from gravity data. In this context, we present new 3D density and velocity models of the Fennoscandian upper-mantle. These models were obtained by performing a non linear joint inversion of both teleseismic and gravity data. To ensure a good agreement between recovered models, we assumed a depth dependent linear relationship linking density and velocity perturbations according to Birch's law, which was also inverted. We computed 3315 teleseismic P-delay times from 54 events recorded by the dense SVEKALAPKO experiment (140 seismometers) deployed around the transition zone between Proterozoic and Archean domains in Finland. Gravity data consist in Bouguer anomalies covering the whole Finland and were provided by the National Gravity net of the Finnish Geodetic Institute and processed by the Geological Survey of Finland. As the Fennoscandian crust is well known from previous studies, we also corrected both data set for crustal effects. Consistent inversion regularisation was found through cost functions analysis. Besides, to assess the accuracy of our results, we carried out different sensitivity tests. Resulting models show significant velocity (3%) and density (100 kg/m³) perturbations with a quite good resolution down to 350 km. Globally, models are in good agreement except for shallower layers. This study supports the assumptions that (1) uppermost mantle is governed by mantle heterogeneities which matches crustal segment (until at least 150 km in depth) and should be

  9. The Effect of Pre-Impact Porosity and Vertical Density Gradients on the Gravity Signature of Lunar Craters as Seen by GRAIL

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, H. J.; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Nimmo, F.; Phillips, R. J.; Bierson, C. J.; Zuber, M. T.

    2015-09-01

    We use iSALE to model complex crater formation on the Moon. We vary initial target porosity and model vertical density/porosity gradients in the crust. We calculate the Bouguer anomaly associated with the craters and match them to GRAIL observations.

  10. A gravity survey of parts of quadrangles 26E, 26F, 27E, and 27F, northeastern Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Miller, C.H.; Showail, A.A.; Kane, M.F.; Khoja, I.A.; Al Ghandi, S. A.

    1989-01-01

    The greatest complete Bouguer anomaly is associated with basaltic lava flows located in the northeastern part of the survey area. The thickness of the basalt in outcrop does not account for the anomalies with the highest amplitudes, but the latter may be due to the presence of a basalt-filled vent. Those anomalies that are present do not define the basalt flows well, but the largest free-air anomaly occurs over the southwestern margin of the Salma Caldera, located about 15 km from the basalt flows. The source of the free-air anomaly is unknown, but it may be related to another hidden basaltic vent.

  11. 3-D density modeling of Mt. Paekdu (N Korea/China) stratovolcano and its evolution by a combination of EGM2008/terrestrial gravity field

    NASA Astrophysics Data System (ADS)

    Götze, Hans-Jürgen; Choi, Sungchan

    2015-04-01

    We combined the global gravity dataset EGM2008 and a local terrestrial gravity data survey to conduct constrained 3-D crustal density modeling of a strato-volcanic complex and the surrounding area located close to the border of North Korea and China. The independent geophysical (seismic, seismology, geochemistry) and petrological constraints will be presented together with the preprocessing of data base by curvature analysis and Euler deconvolution. The multiple data base is used to assist a general interpretation of the investigated area, and the 3D density model (modelled by the in-house IGMAS+ software). Mt. Paekdu is characterized by a low of Bouguer anomaly of some -110 × 10-5 m/s2, which is caused by the combined gravity effects of (1) Moho depth of about 40 km, (2) a zone with both lower P-wave velocity and density than the surrounding, (3) low density volcanic rocks at the surface, and (4) the presence of a magma chamber that has not previously been identified. The terrestrial gravity field measured along the seismic profile shows a remarkable anomaly descending from the southern- to the northern flank of the Mt. Paekdu volcano, which should be a typical anomaly pattern generally observed over the active volcanic area in the world (e.g. the Yellow Stone volcano). The trend is interpreted to be caused by a prominent density difference between a serious of high density mid crustal sill beneath the southern flank and a predicted partial melted zone locating in the northern flank. With the help of several geoscientific observations (seismic, electromagnetic, gravity and geochemistry) and the 3D density model we conclude that a high density sill was formed in Pliocene and early Pleistocene after pre-shield plateau-forming eruption. Since the Pliocene, volcanic activity in the Mt. Paekdu region might be migrated from the southeastern of North Korea to the northwest, following the path of NW-SE-trending faults. Recently observed seismic tremors can be explained

  12. 3-D Density Modeling of the Combined EGM2008/Terrestrial Gravity Field over the Mt. Paekdu (N Korea/China) Stratovolcano and Its Evolution

    NASA Astrophysics Data System (ADS)

    Goetze, H. J.; Choi, S.

    2014-12-01

    In the presentation we get use of the global gravity dataset EGM2008 and a local terrestrial gravity data survey for a constrained 3-D crustal density modeling of a stratovolcano and its surrounding area located close to the border of North Korea and China. The independent geophysical (seismic, seismology, geochemistry) and petrological constraints will be presented together with the preprocessing of data base by curvature analysis and Euler deconvolution. The multiple data base is used to assist a general interpretation of the investigated area in time, and the 3D density model (modelled by the inhouse IGMAS+ software). Mt. Paekdu is characterized by a low of Bouguer anomaly of some -110 ´ 10-5 m/s2, which is caused by the combined gravity effects of (1) Moho depth of about 40 km, (2) a zone with both lower P-wave velocity and density than the surrounding, (3) low density volcanic rocks at the surface, and (4) the presence of a magma chamber that has not previously been identified. The terrestrial gravity field measured along the seismic profile shows a remarkable anomaly descending from the southern- to the northern flank of the Mt. Paekdu volcano, which should be a typical anomaly pattern generally obsered over the active volcanic area in the world (e.g. the Yellow Stone volcano). The trend is interpreted to be caused by a prominent density difference between a serious of high density mid crustal sill beneath the southern flank and a predicted partial melted zone locating in the northern flank. With the help of several geoscientific observations (seismic, electromagnetic, gravity and geochemistry) and the 3D density model we conclude that a high density sill was formed in Pliocene and early Pleistocene after pre-shield plateau-forming eruption. Since the Pliocene, volcanic activity in the Mt. Paekdu region might be migrated from the southeastern of North Korea to the northwest, following the path of NW-SE-trending faults. Recently observed seismic tremors can

  13. Structure of the lithosphere below the southern margin of the East European Craton (Ukraine and Russia) from gravity and seismic data

    NASA Astrophysics Data System (ADS)

    Yegorova, T. P.; Stephenson, R. A.; Kostyuchenko, S. L.; Baranova, E. P.; Starostenko, V. I.; Popolitov, K. E.

    2004-03-01

    The present study was undertaken with the objective of deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the East European Craton (EEC). The study area includes the inverted southernmost part of the intracratonic Dnieper-Donets Basin (DDB)-Donbas Foldbelt (DF), its southeastern prolongation along the margin of the EEC-the sedimentary succession of the Karpinsky Swell (KS), the southwestern part of the Peri-Caspian Basin (PCB), and the Scythian Plate (SP). These structures are adjacent to a zone, along which the crust was reworked and/or accreted to the EEC since the late Palaeozoic. In the Bouguer gravity field, the southern margin of the EEC is marked by an arc of gravity highs, correlating with uplifted Palaeozoic rocks covered by thin Mesozoic and younger sediments. A three-dimensional (3D) gravity analysis has been carried out to investigate further the crustal structure of this area. The sedimentary succession has been modelled as two heterogeneous layers—Mesozoic-Cenozoic and Palaeozoic—in the analysis. The base of the sedimentary succession (top of the crystalline Precambrian basement) lies at a depth up to 22 km in the PCB and DF-KS areas. The residual gravity field, obtained by subtracting the gravitational effect of the sedimentary succession from the observed gravity field, reveals a distinct elongate zone of positive anomalies along the axis of the DF-KS with amplitudes of 100-140 mGal and an anomaly of 180 mGal in the PCB. These anomalies are interpreted to reflect a heterogeneous lithosphere structure below the supracrustal, sedimentary layers: i.e., Moho topography and/or the existence of high-density material in the crystalline crust and uppermost mantle. Previously published data support the existence of a high-density body in the crystalline crust along the DDB axis, including the DF, caused by an intrusion of mafic and

  14. Understanding Conspicuous Gravity Low Over the Koyna-Warna Seismogenic Region (Maharashtra, India) and Earthquake Nucleation: A Paradigm Shift

    NASA Astrophysics Data System (ADS)

    Vasanthi, A.; Satish Kumar, K.

    2016-06-01

    The continued seismicity in Koyna-Warna region of the western part of Maharastra (India) and its relationship with subsurface structures, concealed below thick volcanic sequences, are studied in detail using gravity field along with newly available deep scientific drilling results. This seismically active zone is marked by a large conspicuous negative gravity anomaly, the causes of which are yet to be fully understood. Recent findings from the boreholes drilled in the Koyna (G upta et al. in Int J Earth Sci 104:1511-1522, 2015) and Killari seismic zones, both of which penetrated the thick Deccan volcanic cover and the underlying Archean crystalline basement, have motivated us to revisit the Bouguer gravity field over this region, using a newly developed finite element method of regional-residual separation. Our study reveals the presence of two thick low-density/low-velocity crustal zones below the Koyna-Warna region, the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the Moho. Both of these zones appear to contain mantle-metasomatised and fractionated magmatic material, respectively. Interestingly, the hypocenters of all M ≥ 5 Koyna earthquakes occur within the upper low-velocity/low-density zone. We also suggest high-order crustal exhumation below this region, which led to the removal of the entire sedimentary and granitic upper crustal column. This process has brought denser mid-crustal lithological facies close to the surface. Quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing. A paleo-rift may have existed beneath this region below which Moho temperatures (~600 °C) and mantle heat flow (~31 mW/m2) are still high.

  15. Understanding Conspicuous Gravity Low Over the Koyna-Warna Seismogenic Region (Maharashtra, India) and Earthquake Nucleation: A Paradigm Shift

    NASA Astrophysics Data System (ADS)

    Vasanthi, A.; Satish Kumar, K.

    2016-02-01

    The continued seismicity in Koyna-Warna region of the western part of Maharastra (India) and its relationship with subsurface structures, concealed below thick volcanic sequences, are studied in detail using gravity field along with newly available deep scientific drilling results. This seismically active zone is marked by a large conspicuous negative gravity anomaly, the causes of which are yet to be fully understood. Recent findings from the boreholes drilled in the Koyna (Guc(upta) et al. in Int J Earth Sci 104:1511-1522, 2015) and Killari seismic zones, both of which penetrated the thick Deccan volcanic cover and the underlying Archean crystalline basement, have motivated us to revisit the Bouguer gravity field over this region, using a newly developed finite element method of regional-residual separation. Our study reveals the presence of two thick low-density/low-velocity crustal zones below the Koyna-Warna region, the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the Moho. Both of these zones appear to contain mantle-metasomatised and fractionated magmatic material, respectively. Interestingly, the hypocenters of all M ≥ 5 Koyna earthquakes occur within the upper low-velocity/low-density zone. We also suggest high-order crustal exhumation below this region, which led to the removal of the entire sedimentary and granitic upper crustal column. This process has brought denser mid-crustal lithological facies close to the surface. Quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing. A paleo-rift may have existed beneath this region below which Moho temperatures (~600 °C) and mantle heat flow (~31 mW/m2) are still high.

  16. Gravity and crustal structure

    NASA Technical Reports Server (NTRS)

    Bowin, C. O.

    1976-01-01

    Lunar gravitational properties were analyzed along with the development of flat moon and curved moon computer models. Gravity anomalies and mascons were given particular attention. Geophysical and geological considerations were included, and comparisons were made between the gravitional fields of the Earth, Mars, and the Moon.

  17. Satellite Magnetic Anomalies of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator); Olivier, R.

    1984-01-01

    Preliminary MAGSAT scalar magnetic anomaly data of Africa, Europe, and adjacent marine areas were reduced to the pole assuming a constant inducing Earth's magnetic field of 60,000 nT. This process leads to a consistent anomaly data set free from marked variations in directional and intensity effects of the Earth's magnetic field over this extensive region. The resulting data are correlated with long wave length-pass filtered free-air gravity anomalies; regional heat flow, and tectonic data to investigate magatectonic elements and the region's geologic history. Magnetic anomalies are related to both ancient as well as more recent Cenozoic structural features.

  18. Crustal Structure in the Southern Rockall Trough from Satellite Gravity Data: Evidence for Sea-floor Spreading

    NASA Astrophysics Data System (ADS)

    Chappell, A.; Kusznir, N. J.

    2005-05-01

    The southern Rockall Trough south of 57 N has previously been interpreted as either an intra-continental rift floored with highly extended continental crust, or a failed oceanic rift formed by Cretaceous sea floor spreading. Satellite gravity, bathymetry data and seismic estimates of sediment thickness are used to derive crustal basement thickness for the southern Rockall Trough and adjacent regions using a gravity inversion method incorporating a correction for the large negative thermal gravity component present in oceanic and stretched continental lithosphere. The marine Bouguer anomaly, derived from satellite free air gravity (Sandwell & Smith 1997) and Gebco 2003 bathymetry data, is inverted using the method of Oldenberg (1974), incorporating an iteratively applied thermal anomaly correction, to give Moho depth. For oceanic crust the thermal anomaly correction is calculated using isochron ages (Muller et al. 1997) and for continental crust from the beta stretching factors resulting from gravity derived crustal basement thickness and an assumed rift age. When sediment thickness and volcanic addition are assumed to be zero, the resulting upper bound of crustal thickness from the gravity inversion is as little as 10 km in the southern Rockall Trough. A segmented axial thickening of the crust at the centre of the Rockall Trough is predicted, between the Barra volcanic ridge and the Anton Dohrn seamount and is interpreted as having a volcanic origin. Inclusion of a sediment thickness correction in the gravity inversion further reduces predicted crustal thickness. A pseudo-sediment-thickness map has been constructed from the available wide-angle data and incorporated in the gravity inversion. The addition of up to 5.5 km of sediment in the gravity inversion reduces the upper bound of crustal thickness to less than 3 km in some locations. The segmented axial thickening and thin crust shown by the gravity inversion, the lack of intra-basinal faulting, and the volcanic

  19. Satellite Gravity Drilling the Earth

    NASA Technical Reports Server (NTRS)

    vonFrese, R. R. B.; Potts, L. V.; Leftwich, T. E.; Kim, H. R.; Han, S.-H.; Taylor, P. T.; Ashgharzadeh, M. F.

    2005-01-01

    Analysis of satellite-measured gravity and topography can provide crust-to-core mass variation models for new insi@t on the geologic evolution of the Earth. The internal structure of the Earth is mostly constrained by seismic observations and geochemical considerations. We suggest that these constraints may be augmented by gravity drilling that interprets satellite altitude free-air gravity observations for boundary undulations of the internal density layers related to mass flow. The approach involves separating the free-air anomalies into terrain-correlated and -decorrelated components based on the correlation spectrum between the anomalies and the gravity effects of the terrain. The terrain-decorrelated gravity anomalies are largely devoid of the long wavelength interfering effects of the terrain gravity and thus provide enhanced constraints for modeling mass variations of the mantle and core. For the Earth, subcrustal interpretations of the terrain-decorrelated anomalies are constrained by radially stratified densities inferred from seismic observations. These anomalies, with frequencies that clearly decrease as the density contrasts deepen, facilitate mapping mass flow patterns related to the thermodynamic state and evolution of the Earth's interior.

  20. Gravity science investigation of Ceres from Dawn

    NASA Astrophysics Data System (ADS)

    Park, Ryan; Konopliv, Alexander; Bills, Bruce; Castillo-Rogez, Julie; Asmar, Sami; Rambaux, Nicolas; Raymond, Carol; Russell, Christopher; Zuber, Maria; Ermakov, Anton; King, Scott; Rayman, Marc

    2016-04-01

    The Dawn gravity science investigation utilizes the DSN radiometric tracking of the spacecraft and on-board framing camera images to determine the global shape and gravity field of Ceres. The gravity science data collected during Approach, Survey, and High-Altitude Mapping Orbit phases were processed. Currently, the latest gravity field called CERES08A is available, which is globally accurate to degree and order 5. Combining the gravity and shape data gives the bulk density of 2162.5±8 kg/m3. The low Bouguer gravity at high topography area, or vice versa, indicates that the surface of Ceres is likely compensated and that its interior presents a low-viscosity layer at depth. The degree 2 gravity harmonics show that the rotation of Ceres is very nearly about a principal axis. This consistent with hydrostatic equilibrium at 1% level, and infers a mean moment of inertia of Ceres is 0.36, implying some degree of central condensation. Based on a simple two-layer model of Ceres and assuming carbonaceous chondrites and hydrostatic equilibrium, the core size is expected to be ~280 km with corresponding average thickness of the outer shell of ~190 km.

  1. Mapping of Basement Faults with Gravity and Magnetic Data at NE Mexico

    NASA Astrophysics Data System (ADS)

    Yutsis, V.; Krivosheya, K.; Tamez Ponce, A.

    2012-04-01

    Northeast Mexico is essentially the juncture of two distinctly different tectono-stratigraphic provinces, the eastern Gulf of Mexico (Coastal Plane, Sierra Madre Oriental) province and the western Pacific Mexico (Rivera plate, Meso-American trench, Sierra Madre Occidental) province (Goldhammer & Johnson, 2001). Tectonic evolution in northeast Mexico is dominated by divergent-margin development associated with the opening of the Gulf of Mexico and overprinted by non-igneous Laramide orogenic effects (Pindell et al., 1988). The structural grain of northeast Mexico consists of Triassic to Liassic fault-controlled basement blocks, the development of which reflects in part late Paleozoic orogenic patterns of metamorphism and igneous intrusion (Wilson, 1990). There are different tectonic provinces which are recognized interpreting the basement and sediment cover of this area: Coahuila block, La Popa sub-basin, Sabinas basin, Burgos basin, Sierra Madre Oriental (Monterrey trough), and Parras basin. Mojave-Sonora megashear and San Marcos fault (Chavez-Cabello et al., 2007) are two principal fault zones crossing the northeast Mexico in NW-SE direction. This paper is presented the integral analysis of the gravity and magnetic data in the northeast Mexico. Complementing with a Digital Model of Elevations (DME) that combined with the review of previous geological studies it serves to compare the surface structures and blocks of basement in this area. Also the separation of the most important tectonic blocks was done, and 2.5D geological-geophysical model was finally developed. This model represents in a general way the principal structural characteristics of northeast Mexico. Gravity and magnetic data analysis was used with purpose to study the structure of the substrata in order to allow modeling of the basement structure and its relation with the sedimentary cover features. The Bouguer gravity and the total field aeromagnetic data were supplied by Geological Survey of Mexico

  2. DOWN'S ANOMALY.

    ERIC Educational Resources Information Center

    PENROSE, L.S.; SMITH, G.F.

    BOTH CLINICAL AND PATHOLOGICAL ASPECTS AND MATHEMATICAL ELABORATIONS OF DOWN'S ANOMALY, KNOWN ALSO AS MONGOLISM, ARE PRESENTED IN THIS REFERENCE MANUAL FOR PROFESSIONAL PERSONNEL. INFORMATION PROVIDED CONCERNS (1) HISTORICAL STUDIES, (2) PHYSICAL SIGNS, (3) BONES AND MUSCLES, (4) MENTAL DEVELOPMENT, (5) DERMATOGLYPHS, (6) HEMATOLOGY, (7)…

  3. Principal facts for a gravity survey made in northeastern Oklahoma and southeastern Kansas during 1948

    USGS Publications Warehouse

    Cook, K.L.; Hoskinson, A.J.; Shelton, G.R.

    1971-01-01

    Observed gravity values, station locations, elevations, theoretical gravity, and free-air anomaly values are provided in tabular form for 554 gravity locations in northeastern Oklahoma-southeastern Kansas.

  4. Constraints on Ceres internal strcuture from the Dawn gravity and shape data

    NASA Astrophysics Data System (ADS)

    Ermakov, A.; Zuber, M. T.; Smith, D. E.; Fu, R. R.; Raymond, C. A.; Russell, C. T.; Park, R. S.

    2015-12-01

    Ceres is the largest body in the asteroid belt with a radius of approximately 470 km. It is large enough to attain a shape much closer to hydrostatic equilibrium than major asteroids. Pre-Dawn shape models of Ceres (e.g. Thomas et al., 2005; Carry et al., 2008) revealed that its shape is consistent with a hydrostatic ellipsoid. After the arrival of the Dawn spacecraft in Ceres orbit in March 2015, Framing Camera images were used to construct shape models of Ceres. Meanwhile, radio-tracking data are being used to develop gravity models. We use the Dawn-derived shape and gravity models to constrain Ceres' internal structure. These data for the first time allow estimation of the degree to which Ceres is hydrostatic. Observed non-hydrostatic effects include a 2.1 km triaxiality (difference between the two equatorial axes) as well as an 660-m center-of-mass - center-of-figure offset. The Dawn gravity data from the Survey orbit shows that Ceres has a central density concentration. Second-degree sectorial gravity coefficients are negatively correlated with topography indicating a peculiar interior structure. We compute the relative crustal thickness based on the observed Bouguer anomaly. Hydrostatic models show that Ceres appears more differentiated based on its gravity than on its shape. We expand the Ceres shape in spherical harmonics, observing that the power spectrum of topography deviates from the power law at low degrees (Fig. 1). We interpret the decrease of power at low degrees to be due to viscous relaxation. We suggest that relaxation happens on Ceres but, unlike modeled in Bland (2013), it is important only at the lowest degrees that correspond to scales of several hundreds of km. There are only a few features on Ceres of that size and at least one of them (an impact basin provisionally named Kerwan) appears relaxed. The simplest explanation is that Ceres's outer shell is not pure ice or pure rock but an ice-rock mixture that allows some relaxation at the

  5. Continental and oceanic magnetic anomalies: Enhancement through GRM

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.

    1985-01-01

    In contrast to the POGO and MAGSAT satellites, the Geopotential Research Mission (GRM) satellite system will orbit at a minimum elevation to provide significantly better resolved lithospheric magnetic anomalies for more detailed and improved geologic analysis. In addition, GRM will measure corresponding gravity anomalies to enhance our understanding of the gravity field for vast regions of the Earth which are largely inaccessible to more conventional surface mapping. Crustal studies will greatly benefit from the dual data sets as modeling has shown that lithospheric sources of long wavelength magnetic anomalies frequently involve density variations which may produce detectable gravity anomalies at satellite elevations. Furthermore, GRM will provide an important replication of lithospheric magnetic anomalies as an aid to identifying and extracting these anomalies from satellite magnetic measurements. The potential benefits to the study of the origin and characterization of the continents and oceans, that may result from the increased GRM resolution are examined.

  6. Regional Geothermal Characterisation of East Anatolia from Aeromagnetic, Heat Flow and Gravity Data

    NASA Astrophysics Data System (ADS)

    Bektaş, Özcan; Ravat, Dhananjay; Büyüksaraç, Aydin; Bilim, Funda; Ateş, Abdullah

    2007-05-01

    East Anatolia is a region of high topography made up of a 2-km high plateau and Neogene and Quaternary volcanics overlying the subduction-accretion complex formed by the process of collision. The aeromagnetic and gravity data surveyed by the Mineral Research and Exploration (MTA) of Turkey have been used to interpret qualitatively the characteristics of the near-surface geology of the region. The residual aeromagnetic data were low-pass filtered and analyzed to produce the estimates of magnetic bottom using the centroid method and by forward modelling of spectra to evaluate the uncertainties in such estimates. The magnetic bottom estimates can be indicative of temperatures in the crust because magnetic minerals lose their spontaneous magnetization at the Curie temperature of the dominant magnetic minerals in the rocks and, thus, also are called Curie point depths (CPDs). The Curie point depths over the region of Eastern Anatolia vary from 12.9 to 22.6 km. Depths computed from forward modelling of spectra with 200 600 km window sizes suggest that the bottom depths from East Anatolia from the magnetic data may have errors exceeding 5 km; however, most of the obtained depths appear to lie in the above range and indicate that the lower crust is either demagnetized or non-magnetic. In the interpretation of the magnetic map, we also used reduction-to-pole (RTP) and amplitude of total gradient of high-pass filtered anomalies, which reduced dipolar orientation effects of induced aeromagnetic anomalies. However, the features of the RTP and the total gradient of the high-pass filtered aeromagnetic anomalies are not highly correlated to the hot spring water locations. On the other hand, many high-amplitude features seen on the total gradient map can be correlated with the ophiolitic rocks observed on the surface. This interpretation is supported by Bouguer gravity data. In this paper, we recommend that the sources of the widespread thermal activity seen in East Anatolia must

  7. On the tectonic problems of the southern East China Sea and adjacent regions: Evidence from gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Shang, Luning; Zhang, Xunhua; Han, Bo; Du, Runlin

    2016-02-01

    In this paper, two sets of gravity and magnetic data were used to study the tectonics of the southern East China Sea and Ryukyu trench-arc system: one data set was from the `Geological-geophysical map series of China Seas and adjacent areas' database and the other was newly collected by R/V Kexue III in 2011. Magnetic and gravity data were reorganized and processed using the software MMDP, MGDP and RGIS. In addition to the description of the anomaly patterns in different areas, deep and shallow structure studies were performed by using several kinds of calculation, including a spectrum analysis, upward-continuation of the Bouguer anomaly and horizontal derivatives of the total-field magnetic anomaly. The depth of the Moho and magnetic basement were calculated. Based on the above work, several controversial tectonic problems were discussed. Compared to the shelf area and Ryukyu Arc, the Okinawa Trough has an obviously thinned crust, with the thinnest area having thickness less than 14 km in the southern part. The Taiwan-Sinzi belt, which terminates to the south by the NW-SE trending Miyako fault belt, contains the relic volcanic arc formed by the splitting of the paleo Ryukyu volcanic arc as a result of the opening of the Okinawa Trough. As an important tectonic boundary, the strike-slip type Miyako fault belt extends northwestward into the shelf area and consists of several discontinuous segments. A forearc terrace composed of an exotic terrane collided with the Ryukyu Arc following the subduction of the Philippine Sea Plate. Mesozoic strata of varying thicknesses exist beneath the Cenozoic strata in the shelf basin and significantly influence the magnetic pattern of this area. The gravity and magnetic data support the existence of a Great East China Sea, which suggests that the entire southern East China Sea shelf area was a basin in the Mesozoic without alternatively arranged uplifts and depressions, and might have extended southwestward and connected with the

  8. Lunar gravity - A harmonic analysis

    NASA Technical Reports Server (NTRS)

    Ferrari, A. J.

    1977-01-01

    A sixteenth-degree and sixteenth-order spherical harmonic lunar gravity field has been derived from the long-term Keplerian variations in the orbits of the Apollo subsatellites and Lunar Orbiter 5. This model resolves the major mascon gravity anomalies of the lunar near side and is in very good agreement with line-of-sight acceleration results. The far-side map shows the major ringed basins to be strong localized negative anomalies located in broad regions of positive gravity which correspond closely to the highlands. The rms pressure levels calculated from equivalent-surface height variations show that the moon and earth support nearly equal pressures, whereas Mars is appreciably stronger. The moon appears to support larger loads than earth owing to its weaker central gravity field and perhaps a colder upper lithosphere. Significant differences between the low-degree gravity and topography spectra indicate that the longer-wavelength topographic features are isostatically compensated.

  9. High-Precise Gravity Observations at Archaeological Sites: How We Can Improve the Interpretation Effectiveness and Reliability?

    NASA Astrophysics Data System (ADS)

    Eppelbaum, Lev

    2015-04-01

    the Lesser Caucasus (western Azerbaijan) under conditions of rugged relief and complex geology. This deposit is well investigated by mining and drilling operations and therefore was used as a reference field polygon for testing this approach. A special scheme for obtaining the Bouguer anomalies has been employed to suppress the terrain relief effects dampening the anomaly effects from the objects of prospecting. The scheme is based on calculating the difference between the free-air anomaly and the gravity field determined from a 3D model of a uniform medium with a real topography. 3-D terrain relief model with an interval of its description of 80 km (the investigated 6 profiles of 800 m length are in the center of this interval) was employed to compute (by the use of GSFC software (Khesin et al., 1996)) the gravitational effect of the medium (σ = 2670 kg/m3). With applying such a scheme the Bouguer anomalies were obtained with accuracy in two times higher than that of TC received by the conventional methods. As a result, on the basis of the improved Bouguer gravity with the precise TC data, the geological structure of the deposit was defined (Khesin et al., 1996). Second approach Second approach was employed at the complex Katekh pyrite-polymetallic deposit, which is located at the southern slope of the Greater Caucasus (northern Azerbaijan). The main peculiarities of this area are very rugged topography of SW-NE trend, complex geology and severe tectonics. Despite the availability of conventional ΔgB (TC far zones were computed up to 200 km), for the enhanced calculation of surrounding terrain topography a digital terrain relief model was created (Eppelbaum and Khesin, 2004). The SW-NE regional topography trend in the area of the Katekh deposit occurrence was computed as a rectangular digital terrain relief model (DTRM) of 20 km long and 600 m wide (our interpretation profile with a length of 800 m was located in the geometrical center of the DTRM). As a whole

  10. Combined gravity and magnetic modeling over Pavagadh and Phenaimata igneous complexes, Gujarat, India: Inference on emplacement history of Deccan volcanism

    NASA Astrophysics Data System (ADS)

    Singh, Bijendra; Prabhakara Rao, M. R. K.; Prajapati, S. K.; Swarnapriya, Ch.

    2014-02-01

    A large number of igneous intrusions related to the Deccan magmatism are exposed in the western and central part of the Indian shield. Gravity and magnetic (G-M) surveys over some of these igneous intrusive bodies depict gravity high and bipolar magnetic anomalies as the most characteristic signatures. The present G-M survey was carried out over the Pavagadh and Phenaimata igneous intrusives. Associated with the Phenaimata complex, Bouguer gravity anomaly shows an elliptical shaped relative gravity high of about 40 mGal and bipolar magnetic anomaly varies from South to North between -800 nT and 1200 nT. The joint G-M modeling reveals the presence of a dense mafic body (2.86 g/cm3). This body is characterized by a remanant magnetization; the related inclination (I) = ˜44° and declination (D) = ˜160° may correspond with the 29R polarity chron of Deccan magnetostratigraphy. Remanant magnetization together with age data suggest that the Phenaimata igneous intrusive emplaced during the end of the main magmatism phase of Deccan. Over the Pavagadh, a circular gravity and magnetic lows of about -15 mGal and -500 nT respectively is reported for the first time which is surrounded by a gravity and magnetic high of about 30 mGal and 350 nT, respectively. The joint G-M modeling over the Pavagadh intrusive reveals the presence of a deep-seated cone shaped high-density (⩾3.0 g/cm3) gabbroic body which might extend up to a great depth. Its top surface reaches up to a depth of about 10.0 km. Overlying this body is a low-density (2.40 g/cm3) rhyolite, which extends up to the surface and is the source for low gravity anomaly. It is surrounded by another high-density (2.89 and 3.02 g/cm3) mafic bodies with reverse remanant magnetization direction (I = ˜38° and D = ˜152°). The modeled direction of remanant magnetization for the rhyolite (I = -32° and D = 336°) and deeper gabbroic (I = -32° and D = 340°) bodies show normal polarity. Measured magnetization direction for the

  11. Trace anomaly driven inflation

    NASA Astrophysics Data System (ADS)

    Hawking, S. W.; Hertog, T.; Reall, H. S.

    2001-04-01

    This paper investigates Starobinsky's model of inflation driven by the trace anomaly of conformally coupled matter fields. This model does not suffer from the problem of contrived initial conditions that occurs in most models of inflation driven by a scalar field. The universe can be nucleated semiclassically by a cosmological instanton that is much larger than the Planck scale provided there are sufficiently many matter fields. There are two cosmological instantons: the four sphere and a new ``double bubble'' solution. This paper considers a universe nucleated by the four sphere. The AdS/CFT correspondence is used to calculate the correlation function for scalar and tensor metric perturbations during the ensuing de Sitter phase. The analytic structure of the scalar and tensor propagators is discussed in detail. Observational constraints on the model are discussed. Quantum loops of matter fields are shown to strongly suppress short scale metric perturbations, which implies that short distance modifications of gravity would probably not be observable in the cosmic microwave background. This is probably true for any model of inflation provided there are sufficiently many matter fields. This point is illustrated by a comparison of anomaly driven inflation in four dimensions and in a Randall-Sundrum brane-world model.

  12. New standards for reducing gravity data: The North American gravity database

    USGS Publications Warehouse

    Hinze, W. J.; Aiken, C.; Brozena, J.; Coakley, B.; Dater, D.; Flanagan, G.; Forsberg, R.; Hildenbrand, T.; Keller, Gordon R.; Kellogg, J.; Kucks, R.; Li, X.; Mainville, A.; Morin, R.; Pilkington, M.; Plouff, D.; Ravat, D.; Roman, D.; Urrutia-Fucugauchi, J.; Veronneau, M.; Webring, M.; Winester, D.

    2005-01-01

    The North American gravity database as well as databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revising procedures for calculating gravity anomalies, taking into account our enhanced computational power, improved terrain databases and datums, and increased interest in more accurately defining long-wavelength anomaly components. Users of the databases may note minor differences between previous and revised database values as a result of these procedures. Generally, the differences do not impact the interpretation of local anomalies but do improve regional anomaly studies. The most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conventionally used geoid or sea level. Principal facts of gravity observations and anomalies based on both revised and previous procedures together with germane metadata will be available on an interactive Web-based data system as well as from national agencies and data centers. The use of the revised procedures is encouraged for gravity data reduction because of the widespread use of the global positioning system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with North American and national databases. Anomalies based on the revised standards should be preceded by the adjective "ellipsoidal" to differentiate anomalies calculated using heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid. ?? 2005 Society of Exploration Geophysicists. All rights reserved.

  13. Position from gravity

    NASA Technical Reports Server (NTRS)

    Mather, R. S.

    1973-01-01

    Procedures for obtaining position from surface gravity observations are reviewed and their relevance assessed in the context of the application of modern geodetic techniques to programs of Earth and ocean physics. Solutions based on the use of surface layer techniques, the discrete value approach, and the development from Green's theorem are stated in summary, the latter being extended to order e cubed in the height anomaly. The representation of the surface gravity field which is required in order that this accuracy may be achieved is discussed. Interim techniques which could be used in the absence of such a representation are also outlined.

  14. Environmental applications of gravity surveying

    SciTech Connect

    Barrows, L.J. ); Nesbit, L.C. ); Khan, W.A. )

    1994-04-01

    The Allis Park Sanitary Landfill Company developed a new landfill near Onway, Michigan in an area which has glacial alluvium and glacial till overlying limestone. There are several solution karst features in the region and some critics had maintained that a new karst collapse could rupture the liner system and allow escape of leachate into the groundwater. The gravity survey was conducted to determine the extent of any karst development at the site. The first portion of the survey was two profiles over some karst features located about five miles southeast of the proposed landfill. These showed negative gravity anomalies. The survey of the proposed landfill site resulted in a 50 microGal contour map of the area and also showed a negative anomaly. This could be due to either elevation variations on the till to limestone bedrock surface or to karst development within the limestone. Because there was no evidence of historic development of new karst features in the region, the gravity anomaly was not further investigated. In another gravity survey, a large retail department store had been remodeled and extended over an area previously occupied by an auto service center. The removal of a waste oil storage tank (UST) had not been documented and the environmental consultant (KEMRON, Inc.) proposed that a gravity survey be used to find the tank location. This proposal was based on calculations of the gravity effects of a UST. The survey resulted in a four-microGal contour map which showed a couple of anomalies which could be due to a tank or a backfilled tank excavation. During the survey, a store employee identified the previous location of the tank and explained that she had personally witnessed its removal. Based on the employee's eye-witness account of the tank removal and the coincidence of her indicated tank location with one of the gravity anomalies the authors recommended the site be granted clean closure.

  15. Regional magnetic anomaly constraints on continental rifting

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  16. Combined magnetic and gravity analysis

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W.; Chandler, V. W.; Mazella, F. E.

    1975-01-01

    Efforts are made to identify methods of decreasing magnetic interpretation ambiguity by combined gravity and magnetic analysis, to evaluate these techniques in a preliminary manner, to consider the geologic and geophysical implications of correlation, and to recommend a course of action to evaluate methods of correlating gravity and magnetic anomalies. The major thrust of the study was a search and review of the literature. The literature of geophysics, geology, geography, and statistics was searched for articles dealing with spatial correlation of independent variables. An annotated bibliography referencing the Germane articles and books is presented. The methods of combined gravity and magnetic analysis techniques are identified and reviewed. A more comprehensive evaluation of two types of techniques is presented. Internal correspondence of anomaly amplitudes is examined and a combined analysis is done utilizing Poisson's theorem. The geologic and geophysical implications of gravity and magnetic correlation based on both theoretical and empirical relationships are discussed.

  17. The RAMESSES experiment-V. Crustal accretion at axial volcanic ridge segments-a gravity study at 57°45'N on the slow spreading Reykjanes Ridge

    NASA Astrophysics Data System (ADS)

    Peirce, Christine; Navin, Debbie A.

    2002-04-01

    Presented in this paper are the results of a two-stage analysis of gravity data acquired during a multidisciplinary geophysical survey of a magmatically active axial volcanic ridge (AVR) segment located at 57°45'N on the Reykjanes Ridge, part of the slow spreading Mid-Atlantic Ridge south of Iceland. Modelling of the free-air anomaly in 2-D shows that, across-axis, the observed anomaly results largely from density and layer thickness variation in the mid-lower crust. Although seismic control on crustal thickness along-axis is limited, modelling also suggests that both crustal density and thickness also vary towards AVR tips. Using the 2-D modelling results as crustal reference, the residual mantle Bouguer anomaly (RMBA) is calculated to assess whether magma-related density anomalies are present in the mantle and to investigate the structure of, and relationship between, adjacent AVRs along-axis. RMBA lows are associated with both an along-ridge trend encompassing a number of adjacent AVRs and with individual, more topographically robust AVRs. Modelling of the RMBA low associated with the 57°45'N AVR further suggests that along-axis density variation is confined to the central region of this AVR and that the anomaly can largely be accounted for by density variation within Layer 3 and a degree of crustal thinning towards AVR tips. The nature of the along-axis variation in crustal density further suggests that it may result from repeated phases of magma supply to the crustal system from the mantle. Within the resolution of the RMBA, modelling does not confirm or preclude the presence of a subcrustal density anomaly associated with retention of a small percentage of melt in the mantle. However, a melt-free model for at least the top 40 km of the mantle is preferred as this is consistent with the results of modelling a coincident magnetotelluric data set. The ridge-trend characteristics of the RMBA also suggest that magma delivery may take place along this trend, and

  18. New Insights into the Tectonics of the Midcontintent of U.S.A. from EarthScope USArray Seismic, Gravity, Magnetic and Heat Flow Datasets

    NASA Astrophysics Data System (ADS)

    Ravat, D.; Zhang, H.; Newman, L. C. C.; Lowry, A. R.

    2015-12-01

    We examine crustal and upper mantle structure and physical parameters from EarthScope USArray receiver functions, seismic tomography, gravity, and magnetic anomaly data to understand the tectonic framework of the midcontinent of the U.S. (New Madrid Seismic Zone/Rift Complex, Illinois Basin, Tennessee-Illinois-Kentucky Lineament (TIKL), and Grenville Front). The neodymium (Nd) crustal formation boundary seen in geochemical and the long-wavelength magnetic anomaly data is not apparent in the crustal or mantle seismic parameters or density. This is not completely surprising since the Nd systematics and magnetization is controlled by accessory minerals rather than bulk physical parameters. The USArray station spacing is not sufficient to capture the density and corresponding magnetic variations associated with mafic plutons except where stations are located over the plutons themselves (e.g., the Bloomfield Pluton). With the standard Moho density contrasts, Vp/Vs based crustal densities, and mantle velocity-density relationships, significant long-wavelength residuals (misfit) between observed and modeled Bouguer gravity anomalies remain over the Illinois Basin, the TIKL, and the Grenville Front in Ohio, extending north into Lake Erie and New York. Jointly inverted USArray receiver functions and gravity based Vp/Vs and the crustal thickness suggest that the Moho in the western Illinois basin and the Grenville Front in Ohio are thicker than previously known (about 50 km). The bottom of the strong crustal magnetization layer is unusually thin (15-20 km) in the New Madrid Seismic Zone, which extends northward from there into Illinois, northern Missouri and Indiana. In the Rough Creek Graben, the magnetic layer thickness is about 40 km, which is consistent with the non-magmatic nature of that branch of the rift. These observation may also imply that the rift related basal crustal layer in the New Madrid Seismic Zone is non-magnetic or very weakly magnetic. The thinner

  19. Unveiling subglacial geology and crustal architecture in the Recovery frontier of East Antarctica with recent aeromagnetic and airborne gravity imaging

    NASA Astrophysics Data System (ADS)

    Ferraccioli, F.; Forsberg, R.; Jordan, T. A.; Matsuoka, K.; Olsen, A.; King, O.; Ghidella, M.

    2014-12-01

    East Antarctica is the least known continent, despite being a keystone in the Gondwana, Rodinia and Columbia supercontinents. Significant progress has been made in recent years in exploring East Antarctica using aeromagnetic and airborne gravity together with radar. Major aerogeophysical campaigns over the Wilkes Subglacial Basin (Ferraccioli et al., 2009 Tectonophysics), the Aurora Subglacial Basin (Aitken et al., 2014 GRL) and the Gamburtsev Subglacial Mountains (Ferraccioli et al., 2011, Nature) provide new glimpses into the crustal architecture of East Antarctica. However, a major sector of the continent that includes key piercing points for reconstructing linkages between East Antarctica and Laurentia within Rodinia, and also the inferred remnants of a major suture zone active during Gondwana amalgamation in Pan-African times (ca 500 Ma), has remained largely terra incognita. Here we present the results of a major aerogeophysical survey flown over this sector of East Antarctica, named the Recovery Frontier, from the major ice stream flowing in the region. The survey was flown during the IceGRAV 2012-13 field season, as part of a Danish-Norwegian-UK and Argentine collaboration and led to the collection of 29,000 line km of radar, laser altimetry, gravity and magnetic data. We present the new aeromagnetic anomaly, Bouguer and residual and enhanced anomaly maps for the region. Using these images we trace the extent of major subglacial faults and interpret these to delineate the tectonic boundaries separating the Coast block, the Shackleton Range and the Dronning Maud Land crustal provinces. Forward magnetic and gravity modelling enables us to examine the inferred Pan-African age suture zone in the Shackleton Range and address its tectonic relationships with older terranes of the Mawson Craton and Grenvillian-age terranes of Dronning Maud Land and interior East Antarctica. Finally, we present new models to test our hypothesis that Paleozoic to Mesozoic rift basins

  20. The mineralogy of global magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1982-01-01

    The Curie Balance was brought to operational stage and is producing data of a preliminary nature. Substantial problems experienced in the assembly and initial operation of the instrument were, for the most part, rectified, but certain problems still exist. Relationships between the geology and the gravity and MAGSAT anomalies of West Africa are reexamined in the context of a partial reconstruction of Gondwanaland.

  1. Farside lunar gravity from a mass point model

    NASA Technical Reports Server (NTRS)

    Ananda, M.

    1975-01-01

    A mass point representation of the lunar gravity field was determined from the long-period orbital variations of the Apollo 15 and 16 subsatellites and Lunar Orbiter V. A radial acceleration contour map, evaluated at 100 km altitude from the lunar surface, shows that the nearside is in close agreement with the result derived from the line of sight method by Muller and Sjogren. The farside map shows the highland regions as broad positive gravity anomaly areas and the basins such as Korolev, Hertzsprung, Moscoviense, Mendeleev, and Tsiolkovsky as localized, negative gravity anomaly regions. The farside map has a first-order agreement with the result derived from the harmonic field method by Ferrari. The mass points analysis indicates that the nearside is almost all negative gravity anomaly regions except for the known positive mass anomaly basins (mascons) and the farside is almost all positive gravity anomaly regions except for some localized negative areas near the basins.

  2. Geopotential field anomalies and regional tectonic features

    NASA Astrophysics Data System (ADS)

    Mandea, Mioara; Korte, Monika

    2016-07-01

    Maps of both gravity and magnetic field anomalies offer crucial information about physical properties of the Earth's crust and upper mantle, required in understanding geological settings and tectonic structures. Density and magnetization represent independent rock properties and thus provide complementary information on compositional and structural changes. Two regions are considered: southern Africa (encompassing South Africa, Namibia and Botswana) and Germany. This twofold choice is motivated firstly by the fact that these regions represent rather diverse geological and geophysical conditions (old Archean crust with strong magnetic anomalies in southern Africa, and much younger, weakly magnetized crust in central Europe) and secondly by our intimate knowledge of the magnetic vector ground data from these two regions. We take also advantage of the recently developed satellite potential field models and compare magnetic and gravity gradient anomalies of some 200 km resolution. Comparing short and long wavelength anomalies and the correlation of rather large scale magnetic and gravity anomalies, and relating them to known lithospheric structures, we generally find a better agreement over the southern African region than the German territory. This probably indicates a stronger concordance between near-surface and deeper structures in the former area, which can be perceived to agree with a thicker lithosphere.

  3. Subsurface structural mapping of Northern Nasser Lake region, Aswan, Egypt, using Bouguer data

    NASA Astrophysics Data System (ADS)

    Saleh, Salah

    2011-01-01

    In this study, we attempt to delineate the subsurface structures for the tectonic active region of Northern Nasser Lake using integrated interpretation techniques of gravity data with seismicity. The depths to the gravity sources, and the locations of the contacts of density contrast were estimated. Two methods were used for estimating source depths and contact locations: horizontal gradient (HG) and Euler deconvolution methods. Moreover, power spectral analysis, bandpass and upward continuation techniques were applied to evaluate the shallow and deep seated structures. Shallow depth structures were ranging between 0.30 km and 0.80 km. However, two average levels (interfaces) at depth 3.1 km and 7.2 km below the measuring level were revealed for the intermediate and deep seated structures respectively. Results of Euler deconvolution method suggested that, in the eastern part of the area, the basement could be observed on the ground and has become deeper in the central part. The interpreted structural map reveals that the area is affected by a set of faults trending mainly in the NW, E-W, N-S and NE-SW directions. Actually, this map has confirmed the idea that the intersections between the N-S and E-W striking faults along Nasser Lake area have generated seismic pulses. Moreover, three seismic zones (Z1, Z2 and Z3) are well correlated with the fault trends of the subsurface structures as derived from the horizontal gradient map. The present results suggest that there exist seismically-active fault east of High Dam, passing throughout Aswan reservoir from north to south. This fault is occupying region of high stress values which may generate large earthquakes in future, as it has long extension over several kilometers. Furthermore, the evaluated intruded volcanic bodies are found almost at the intersections between the E-W and NW oriented faults. Finally, the area is dissected by basement uplifts and troughs controlled mainly by the NW-SE faults.

  4. Gauge anomalies, gravitational anomalies, and superstrings

    SciTech Connect

    Bardeen, W.A.

    1985-08-01

    The structure of gauge and gravitational anomalies will be reviewed. The impact of these anomalies on the construction, consistency, and application of the new superstring theories will be discussed. 25 refs.

  5. ANOMALY STRUCTURE OF SUPERGRAVITY AND ANOMALY CANCELLATION

    SciTech Connect

    Butter, Daniel; Gaillard, Mary K.

    2009-06-10

    We display the full anomaly structure of supergravity, including new D-term contributions to the conformal anomaly. This expression has the super-Weyl and chiral U(1){sub K} transformation properties that are required for implementation of the Green-Schwarz mechanism for anomaly cancellation. We outline the procedure for full anomaly cancellation. Our results have implications for effective supergravity theories from the weakly coupled heterotic string theory.

  6. The Mystery of the Mars North Polar Gravity-Topography Correlation(Or Lack Thereof)

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Sjogren, W. L.; Johnson, C. L.

    1999-01-01

    Maps of moderately high resolution gravity data obtained from the Mars Global Surveyor (MGS) gravity calibration orbit campaign and high precision topography obtained from the Mars Orbiter Laser Altimeter (MOLA) experiment reveal relationships between gravity and topography in high northern latitudes of Mars. Figure 1 shows the results of a JPL spherical harmonic gravity model bandpass filtered between degrees 6 and 50 contoured over a MOLA topographic image. A positive gravity anomaly exists over the main North Polar cap, but there are at least six additional positive gravity anomalies, as well as a number of smaller negative anomalies, with no obvious correlation to topography. Additional information is contained in the original extended abstract.

  7. The elliptic anomaly

    NASA Technical Reports Server (NTRS)

    Janin, G.; Bond, V. R.

    1980-01-01

    An independent variable different from the time for elliptic orbit integration is used. Such a time transformation provides an analytical step-size regulation along the orbit. An intermediate anomaly (an anomaly intermediate between the eccentric and the true anomaly) is suggested for optimum performances. A particular case of an intermediate anomaly (the elliptic anomaly) is defined, and its relation with the other anomalies is developed.

  8. Inversion for sources of crustal deformation and gravity change at the Yellowstone caldera

    SciTech Connect

    Vasco, D.W.; Taylor, C.L. ); Smith, R.B. )

    1990-11-10

    The Yellowstone caldera was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totaling 3,700 km{sup 3} at 2, 1.2, and 0.6 m.y. before present. Its youthful volcanic history, widespread hydrothermal activity, intense seismicity, and extremely high heat flow, in excess of 30 times the continental average, marks the Yellowstone volcanic system as a giant caldera at unrest. Orthometric height increases of the caldera of up to 76 cm, measured from precise leveling surveys from 1923 to 1975-1977, were inverted to determine volume expansion source models for the caldera-wide deformation. For the 1923 to 1977 uplift episode, two regions of expansion were found: (1) in the northern part of the caldera near the Sour Creek resurgent dome of {approximately}0.37 km{sub 3}, and (2) in the southern part of the caldera, near the Mallard Lake resurgent dome of {approximately}0.41 km{sub 3}. Both bodies occur in the upper crust from near-surface depths to 6.0 km, but the largest volume expansions were found in the 3.0-6.0 km depth range. The southern caldera source volume, near the Mallard Lake dome, may extend down to 9.0 km. From 1976 to 1987, nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift. Models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9.0 km and involved a density perturbation greater than +0.002 g/cm{sup 3}. The modeled volumetric sources are in the same general locations as bodies of low P wave velocities, high seismic attenuation, and large negative Bouguer gravity anomalies. It is likely that the modeled volumetric increases were caused by migration of magmas and/or the introduction of large volumes of hydrothermal fluids into the upper crust.

  9. Unravelling internal structures of an alkaline and carbonatite igneous complex by 3D modelling of gravity and magnetic data

    NASA Astrophysics Data System (ADS)

    Andersson, Magnus; Malehmir, Alireza

    2015-04-01

    Alnö igneous complex in central Sweden is among the few rare and largest alkaline and carbonatite ring-shaped intrusions in the world. Recent high-resolution reflection seismic profiles (Andersson et al., 2013) suggest a saucer-shaped magma chamber at about 3 km depth. Study of anisotropy of magnetic susceptibility (AMS) from a number of carbonatite dykes in the complex suggests a combination of laminar magma flow and sheet closure in the waning stage of magma transport for their emplacement (Andersson et al., 2015). Since 2010 and in conjunction with the above-mentioned studies, more than 400 gravity data points have been measured on land and partly on sea-ice. In addition, the Geological Survey of Sweden (SGU) provided about 100 data points. Petrophysical measurements including density and bulk magnetic susceptibility were carried out for more than 250 rock samples; magnetic remanence was measured on 39 of those samples. The measurements for example indicate that induced magnetisation is dominant in the complex and only a few rock samples show high remanent magnetisation (Q ≥ 1). SGU also provided airborne magnetic data (60 m flight altitude and 200 m flight line spacing) covering the complex on land and areas around it in the sea. These data show the complex as (i) a strong positive Bouguer anomaly, around 20 mGal, one of the strongest gravity gradients observed in Sweden, and (ii) a strong positive magnetic anomaly, around 2400 nT, additionally showing clear magnetic structures within the complex and adjacent to it in the sea. 3D inversion of the gravity and magnetic data was then performed using 100 m by 100 m meshes in the lateral direction and vertically varying meshes starting from 10 m at surface and increasing to 100 m in the depth interval 4250 - 8250 m. The inversion models cover an area of 17 km by 18 km. Regional fields were removed using a first-order polynomial surface for the gravity data and a constant (IGRF) for the magnetic data. Background

  10. The Effect of Pre-Impact Porosity and Vertical Density Gradients on the Gravity Signature of Lunar Craters

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth S.; Blair, David M.; Soderblom, Jason M.; Nimmo, Francis; Phillips, Roger J.; Bierson, Carver J.; Zuber, Maria T.

    2015-11-01

    As a result of NASA’s dual spacecraft Gravity Recovery And Interior Laboratory (GRAIL) mission [Zuber et al., 2013; doi:10.1126/science.1231507], we now know that the lunar crust is highly porous and that the porosity varies laterally [Wieczorek et al., 2013; doi:10.1126/science.1231530] and vertically [Besserer et al., 2014; doi:10.1002/2014GL060240]. Analysis of complex craters located within the lunar highlands reveals that: 1) craters larger than diameter D~210 have positive Bouguer Anomalies (BAs), 2) craters with D ≲ 100 km have both positive and negative BAs that vary about the (near 0) mean by approximately ± 25 mGal, and, 3) D and BA are anticorrelated for craters with D ≲ 100 km [Soderblom et al., 2015; doi:10.1002/2015GL065022]. Numerical modeling by Milbury et al. [2015, LPSC] shows that pre-impact porosity is the dominant influence on the gravity signature of complex craters with D ≲ 100 km, and mantle uplift dominates the gravity for those with D > 140 km. Phillips et al. [2015, LPSC] showed that complex craters located in the South Pole-Aitken (SPA) basin tend to have more-negative BAs than similar craters in the highlands. We use the iSALE hydrocode including pore space compaction [Wünnemann et al., 2006; doi:10.1016/j.icarus.2005.10.013] and dilatant bulking [Collins, 2014; doi:10.1002/2014JE004708] to understand how the gravity signature of impact craters develop. In this study we vary crustal porosity with depth. We find that simulations that have constant porosity with depth have a lower BA for a given crater diameter than those with the same mean porosity, but that vary with depth. We used two different mean porosities (7% and 14%) and found that the BA increases with increasing porosity, similar to simulations with constant porosity. We reproduce the observed anticorrelation between BA and D for D ≲ 100 km only for simulations where the pre-impact porosity is zero or low. Our results support the observation that SPA has lower

  11. Crustal structure of an intraplate thrust belt: The Iberian Chain revealed by wide-angle seismic, magnetotelluric soundings and gravity data

    NASA Astrophysics Data System (ADS)

    Seillé, Hoël; Salas, Ramon; Pous, Jaume; Guimerà, Joan; Gallart, Josep; Torne, Montserrat; Romero-Ruiz, Ivan; Diaz, Jordi; Ruiz, Mario; Carbonell, Ramon; Mas, Ramón

    2015-11-01

    The Iberian Chain is a Cenozoic intraplate thrust belt located within the Iberian plate. Unlike other belts in the Iberia Peninsula, the scarcity of geophysical studies in this area results in a number of unknowns about its crustal structure. The Iberian Chain crust was investigated by means of a NE-SW refraction/wide-angle reflection seismic transect and two magnetotelluric profiles across the chain, oriented along the same direction. The seismic profile was designed to sample the crust by means of three shots designed to obtain a reversed profile. The resulting velocity-depth model shows a moderate thickening of the crust toward the central part of the profile, where crustal thickness reaches values above 40 km, thinning toward de SW Tajo and NE Ebro foreland basins. The crustal thickening is concentrated in the upper crust. The seismic results are in overall agreement with regional trends of Bouguer gravity anomaly and the main features of the seismic model were reproduced by gravity modeling. The magnetotelluric data consist of 39 sites grouped into two profiles, with periods ranging from 0.01 s to 1000 s. Dimensionality analyses show significant 3D effects in the resistivity structure and therefore we carried out a joint 3D inversion of the full impedance tensor and magnetic transfer functions. The Mesozoic and Cenozoic basins along the Chain are well characterized by shallow high conductive zones and low velocities. Elongated conductors reaching mid-crustal depths evidence the presence of major faults dominating the crustal structure. The results from the interpretation of these complementary geophysical data sets provided the first images of the crustal structure of the Iberian Chain. They are consistent with a Cenozoic shortening responsible of the upper crust thickening as well as of the uplift of the Iberian Chain and the generation of its present day topography.

  12. US Aeromagnetic and Satellite Magnetic Anomaly Comparisons

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W. (Principal Investigator); Sexton, J. L.

    1984-01-01

    Scalar aeromagnetic data obtained by the U.S. Naval Oceanographic Office (NOO) Vector Magnetic Survey of the conterminous U.S. were screened for periods of intense diurnal magnetic activity and reduced to anomaly form, filtered, and continued upward. A number of correlations between the NOO, POGO and preliminary MAGSAT data are evident at satellite elevations, including a prominent transcontinental magnetic high which extends from the Anadarko Basin to the Cincinnati Arch. The transcontinental magnetic high is breached by negative anomalies located over the Rio Grande Rift and Mississippi River Aulacogen. Differentially reduced-to-pole NOO and POGO magnetic anomaly data show that the transcontinental magnetic high corresponds to a well-defined regional trend of negative free-air gravity and enhanced crustal thickness anomalies.

  13. New large-scale lithospheric model of the Western Carpathian-Pannonian Basin region based on the 3-D gravity modelling.

    NASA Astrophysics Data System (ADS)

    Alasonati Tasarova, Zuzana; Bielik, Miroslav; Götze, Hans-Jürgen; Afonso, Jaun Carlos; Fullea, Javier

    2010-05-01

    A 3-D forward modelling of the Bouguer gravity field was performed for the Western Carpathian-Pannonian Basin region. The gravity model extends to depth of 220 km and includes also the surrounding units (the Eastern Alps, Bohemian Massif, Trans-European Suture Zone and East European Craton). It is constrained by seismic models, mainly from the CELEBRATION 2000 seismic experiment, and other geophysical data. Additionally, the density distribution and thermal structure in the shallow upper mantle were estimated using a combination of petrological, geophysical, and mineral physics information (LitMod). This approach is necessary in order to better constrain the more complicated structure of the Pannonian Basin. As a result, we present the first 3-D gravity model of the region that combines various geophysical datasets and is consistent with petrological data. Realistic density values within the uppermost mantle provide a better control on the regional gravity signal. In turn, this generates a model with refined and enhanced crustal structure. This means that deeper parts of the model are better accounted for, which helps to better constrain the nature of shallower crustal layers. Although not commonly applied in potential field modelling, we find that this approach is advantageous when modelling large areas with insufficient near-surface constraints. Also, a density distribution within the crust and uppermost mantle that is consistent with petrological data allows better estimates of the depth to the Moho (where it is not constrained by seismic data) and to the lithosphere-asthenosphere boundary. Hence, our model provides improved estimates of both the density distribution within the crust and uppermost mantle and the depth to major density discontinuities (sediments, Moho, lithosphere-asthenosphere boundary). The results of the modelling reveal a markedly different nature of the Western Carpathian-Pannonian region (ALACAPA and Tisza-Dacia microplates) from the

  14. Magnetotelluric deep soundings, gravity and geoid in the south São Francisco craton: Geophysical indicators of cratonic lithosphere rejuvenation and crustal underplating

    NASA Astrophysics Data System (ADS)

    Pinto, Luis Gustavo Rodrigues; de Pádua, Marcelo Banik; Ussami, Naomi; Vitorello, Ícaro; Padilha, Antonio Lopes; Braitenberg, Carla

    2010-09-01

    In the south São Francisco craton a circular and 8-m amplitude geoid anomaly coincides with the outcropping terrain of an Archean-Paleoproterozoic basement. Broadband magnetotelluric (MT) data inversions of two radial profiles within the positive geoid and Bouguer gravity anomaly yield geo-electrical crustal sections, whereby the lower crust is locally more conductive (10 to 100 Ωm) in spatial coincidence with a denser lower crust modeled by the gravity data. This anomalous lower crust may have resulted from magmatic underplating, associated with Mesoarchean and Proterozoic episodes of tholeiitic dike intrusion. Long-period MT soundings reveal a low electrical resistivity mantle (20 to 200 Ωm) from depths beyond 120 km. Forward geoid modeling, using the scope of the low electrical resistivity region within the mantle as a constraint, entails a density increase (40 to 50 kg/m 3) possibly due to Fe enrichment of mantle minerals. However, this factor alone does not explain the observed resistivity. A supplemented presence of small amounts of percolated carbonatite melting (~ 0.005 vol.%), dissolved water and enhanced oxygen fugacity within the peridotitic mantle are viable agents that could explain the less resistive upper mantle. We propose that metasomatic processes confined in the sub-continental lithospheric mantle foster the conditions for a low degree melting with variable CO 2, H 2O and Fe content. Even though the precise age of this metasomatism is unknown it might be older than the Early Cretaceous based on the evidence that a high-degree of melting in a lithospheric mantle impregnated with carbonatites originated the tholeiitic dike intrusions dispersed from the southeastern border of the São Francisco craton, during the onset of the lithosphere extension and break-up of the western Gondwana. The proxies are the NE Paraná and Espinhaço (130 Ma, Ar/Ar ages) tholeiitic dikes, which contain (~ 3%) carbonatites in their composition. The occurrence of a

  15. A regional gravity survey of the Cuyuna Iron Range, Minnesota

    USGS Publications Warehouse

    Durfee, George Austin

    1957-01-01

    A regional gravity survey of the Cuyuna Iron Range, Minnesota, was conducted during the summer of 1955 by the U. S. Geological Survey. It was believed that gravity data would aid in the understanding of the major structures of the range. It was found that synclinal and steeply dipping structures produced positive gravity anomalies while anilclinal structures produced negative anomalies. This principle was noted in areas of well known geology and then applied to outlying areas of the district. The outstanding gravity feature is a narrow positive anomaly extending from south of Brainerd eastward through Aitkin, the axis of the anomaly being somewhat south of the South Range. This gives support to the theory that the Biwabik formation passes under the stratigraphically higher South Range member as a synclinal structure. However, this anomaly is also explained using one main iron formation and assuming an anticlinal structure between the North and South Ranges and a syncline between the South Range and Bay Lake. A large magnitude negative gravity anomaly north of Mille Lacs is postulated to result from an intrusive mass extending to the erosion surface. Aeromagnetics are used to strengthen the gravity interpretation. The need is realized for additional regional gravity coverage to the east of the area Included in this survey and a detailed gravity study of the area between the North and South Ranges.

  16. Gravity Waves

    Atmospheric Science Data Center

    2013-04-19

    article title:  Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...

  17. Techniques for interpretation of geoid anomalies

    NASA Technical Reports Server (NTRS)

    Chapman, M. E.

    1979-01-01

    For purposes of geological interpretation, techniques are developed to compute directly the geoid anomaly over models of density within the earth. Ideal bodies such as line segments, vertical sheets, and rectangles are first used to calculate the geoid anomaly. Realistic bodies are modeled with formulas for two-dimensional polygons and three-dimensional polyhedra. By using Fourier transform methods the two-dimensional geoid is seen to be a filtered version of the gravity field, in which the long-wavelength components are magnified and the short-wavelength components diminished.

  18. The characteristics of neogene sediments and structures in the Siberuang Area (Central Sumatra, Indonesia) based on gravity data

    SciTech Connect

    Santoso, D. )

    1994-07-01

    Neogene sediments in the Siberuang area consist of the Sihapas, Telisa, and Petani formations. The Sihapas Formation is a friable, white to brown sandstone with intercalated claystones, siltstones, and some coal layers. It was deposited in channels or bars of a braided-stream system during early Miocene N4-N8 times. The Telisa Formation, which unconformably overlies the Sihapas Formation, is a calcareous claystone with intercalated glauconitic sands and limestone lenses deposited in a middle to outer neritic environment during middle Miocene N8-N10 times. The Petani Formation is a claystone containing clasts of terrestrial material with some coal lenses and tuffs in the upper part of the section. It is a regressive sequence deposited in an outer neritic environment. These Neogene sediments lie unconformably above the Paleogene Pematang Formation, which is mainly composed of brown conglomerate and conglomeratic sandstones. The Pematang Formation lies unconformably above pre-Tertiary rocks. A Bouguer gravity map processed using a density value of 1.9 gm/cc reveals anomalies with wavelengths of 10 and 15 km. Moving average filtering has been applied to make a regional-residual separation. Map interpretation and modeling along a profile run northeast across the structural trend of the region and indicate a graben-type structure with Neogene sediment thickness increasing from 600 m in the northeast to 2800 m in the southwest. Greatest sediment thickness is attained in the center of the graben, which is delineated by northeast-dipping faults southwest of the area and southwest-dipping faults northeast of the area.

  19. A wavelet transformation approach for multi-source gravity fusion: Applications and uncertainty tests

    NASA Astrophysics Data System (ADS)

    Bai, Yongliang; Dong, Dongdong; Wu, Shiguo; Liu, Zhan; Zhang, Guangxu; Xu, Kaijun

    2016-05-01

    Gravity anomalies detected by different measurement platforms have different characteristics and advantages. There are different kinds of gravity data fusion methods for generating single gravity anomaly map with a rich and accurate spectral content. Former studies using wavelet based gravity fusion method which is a newly developed approach did not pay more attention to the fusion uncertainties. In this paper, we firstly introduce the wavelet based gravity fusion method, and then apply this method to one synthetic model and also to the northern margin of the South China Sea. Wavelet type and the decomposition level are two input parameters for this fusion method, and the uncertainty tests show that fusion results are more sensitive to wavelet type than the decomposition level. The optimal application result of the fusion methodology on the synthetic model is closer to the true anomaly field than either of the simulated shipborne anomaly and altimetry-based anomaly grid. The best fusion result on the northern margin of the South China Sea is based on the 'rbio1.3' wavelet and four-level decomposition. The fusion result contains more accurate short-wavelength anomalies than the altimetry-based gravity anomalies along ship tracks, and it also has more accurate long wavelength characteristics than the shipborne gravity anomalies between ship tracks. The real application case shows that the fusion result has better correspondences to the seafloor topography variations and sub-surface structures than each of the two input gravity anomaly maps (shipborne based gravity anomaly map and altimetry based gravity anomaly map). Therefore, it is possible to map and detect more precise seafloor topography and geologic structures by the new gravity anomaly map.

  20. Three-dimensional gravity ideal body studies in rough terrain

    SciTech Connect

    Ander, M.E.; Huestis, S.P.

    1985-01-01

    An approach to the interpretation of potential field anomaly data is to maximize or minimize some non-linear scalar property of solutions fitting the data. As an example, a comparison of 2-D and 3-D gravity ideal body results from the Lucero Uplift, a westward-tilted fault block located on the western flank of the Rio Grande rift, is discussed. The anomaly was analyzed to obtain bounds on the density contrast, depth of burial, and minimum thickness of its sources. Based on a synthesis of the gravity data with structural analysis and geomorphology, a shallow mafic intrusion is proposed to account for the positive gravity anomaly. 12 refs. (ACR)

  1. Study on crustal magnetic anomalies and Curie surface in Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Gao, Guoming; Kang, Guofa; Bai, Chunhua; Wen, Limin

    2015-01-01

    In this paper, the Potsdam model POMME-6.2 is used to investigate the distributions of crustal magnetic anomalies and Curie surface in Southeast Tibet. The Curie surface is compared with the regional heat flow, Bouguer anomaly, Moho depth, and seismicity. The results show that the magnetic anomalies and Curie surface are both consistent with the geological structure. Sichuan Basin exhibits a high positive anomaly, while orogenic belts such as the Longmenshan, northwestern Sichuan, and western Yunnan, exhibit weak positive or negative anomalies. The distribution of magnetic anomaly confirms that escape flow from east Tibet branches into northeastward part and southward part on west Sichuan Basin, due to resistance by the rigid basin. The depth of Curie surface ranges from 20 to 34 km. The Curie surface beneath the Longmenshan, Xiaojiang and Lijiang-Xiaojinhe faults is shallow, with the uplift strike consistent with the faults. The Curie surface beneath Sichuan Basin and the central Bayan Har massif is deep, with sheet-like depressions. Strong earthquakes primarily occurred in the areas with the uplift of Curie surface. The heat flow values near Tengchong, Lijiang, Dali and Kunming are high and the Curie surface there is shallow.

  2. Potential causes of absolute gravity changes in Taiwan over 2004-2014

    NASA Astrophysics Data System (ADS)

    Kao, R.; Hwang, C.; Kim, J. W.; Masson, F.; Mouyen, M.

    2015-12-01

    We use absolute gravimeter (AG) and GPS observations collected from 2004 to 2014 in Taiwan to identify mass changes in connection to Moho deepening, volcanism, subsidence, earthquake and plate collision. The gravity observations are measured at sites of different geological settings under the AGTO and NGDS projects. The resulting gravity changes cannot be fully explained by vertical motions derived from GPS. Unlike previous AG gravity studies in Taiwan, we apply hydrology-induced gravity changes to raw gravity measurements using a simple model that estimates the Bouguer gravity effect due to rainfalls. Typhoon Morakot, occurring on August 8, 2009, results in torrential rainfalls and large debris flows in southern Taiwan. Morakot causes a gravity increase of 51.22 μGal near an AG site along the southern cross-island highway. The M7.0 Hengchun earthquake on December 26, 2006 causes a gravity rise of 2.32 μGal at the KDNG AG site near its epicenter. A Moho thickening rate (-0.81 μGal/yr) in central Taiwan and a deep-fault slip rate (-0.94 μGal/yr) in eastern Taiwan are postulated from the gravity changes. Other distinct gravity changes are potentially associated with the subsidence in Yunlin County (-2.73 μGal/yr), the magma coolings in Tatun Volcano Group (0.12 μGal/yr), Green Island (-2.95 μGal/yr) and Orchid Island (-0.97μGal/yr).

  3. 2006 Compilation of Alaska Gravity Data and Historical Reports

    USGS Publications Warehouse

    Saltus, Richard W.; Brown, Philip J., II; Morin, Robert L.; Hill, Patricia L.

    2008-01-01

    Gravity anomalies provide fundamental geophysical information about Earth structure and dynamics. To increase geologic and geodynamic understanding of Alaska, the U.S. Geological Survey (USGS) has collected and processed Alaska gravity data for the past 50 years. This report introduces and describes an integrated, State-wide gravity database and provides accompanying gravity calculation tools to assist in its application. Additional information includes gravity base station descriptions and digital scans of historical USGS reports. The gravity calculation tools enable the user to reduce new gravity data in a consistent manner for combination with the existing database. This database has sufficient resolution to define the regional gravity anomalies of Alaska. Interpretation of regional gravity anomalies in parts of the State are hampered by the lack of local isostatic compensation in both southern and northern Alaska. However, when filtered appropriately, the Alaska gravity data show regional features having geologic significance. These features include gravity lows caused by low-density rocks of Cenozoic basins, flysch belts, and felsic intrusions, as well as many gravity highs associated with high-density mafic and ultramafic complexes.

  4. Lymphatic Anomalies Registry

    ClinicalTrials.gov

    2016-07-26

    Lymphatic Malformation; Generalized Lymphatic Anomaly (GLA); Central Conducting Lymphatic Anomaly; CLOVES Syndrome; Gorham-Stout Disease ("Disappearing Bone Disease"); Blue Rubber Bleb Nevus Syndrome; Kaposiform Lymphangiomatosis; Kaposiform Hemangioendothelioma/Tufted Angioma; Klippel-Trenaunay Syndrome; Lymphangiomatosis

  5. A combined magnetometry and gravity study across Zagros orogeny in Iran

    NASA Astrophysics Data System (ADS)

    Abedi, Maysam; Oskooi, Behrooz

    2015-11-01

    the Urumieh-Dokhtar Magmatic Assemblage (UDMA). The UDMA zone increases the magnetic and the Bouguer anomalies by intruding into the CD zone as well.

  6. Accurate Determination of the TOA Solar Spectral NIR Irradiance Using a Primary Standard Source and the Bouguer-Langley Technique

    NASA Astrophysics Data System (ADS)

    Bolsée, D.; Pereira, N.; Decuyper, W.; Gillotay, D.; Yu, H.; Sperfeld, P.; Pape, S.; Cuevas, E.; Redondas, A.; Hernandéz, Y.; Weber, M.

    2014-07-01

    We describe an instrument dedicated to measuring the top of atmosphere (TOA) solar spectral irradiance (SSI) in the near-infrared (NIR) between 600 nm and 2300 nm at a resolution of 10 nm. Ground-based measurements are performed through atmospheric NIR windows and the TOA SSI values are extrapolated using the Bouguer-Langley technique. The interest in this spectral range arises because it plays a main role in the Earth's radiative budget and also because it is employed to validate models used in solar physics. Moreover, some differences were observed between recent ground-based and space-based instruments that take measurements in the NIR and the reference SOLSPEC(ATLAS3) spectrum. In the 1.6 μm region, the deviations vary from 6 % to 10 %. Our measuring system named IRSPERAD has been designed by Bentham (UK) and has been radiometrically characterized and absolutely calibrated against a blackbody at the Belgian Institute for Space Aeronomy and at the Physikalisch-Technische Bundesanstalt (Germany), respectively. A four-month measurement campaign was carried out at the Izaña Atmospheric Observatory (Canary Islands, 2367 m a.s.l.). A set of top-quality solar measurements was processed to obtain the TOA SSI in the NIR windows. We obtained an average standard uncertainty of 1 % for 0.8 μm< λ<2.3 μm. At 1.6 μm, corresponding to the minimum opacity of the solar photosphere, we obtained an irradiance of 234.31±1.29 mWm-2 nm-1. Between 1.6 μm and 2.3 μm, our measurements show a disagreement varying from 6 % to 8 % relative to ATLAS3, which is not explained by the declared standard uncertainties of the two experiments.

  7. Detailed petrophysical characterization enhances geological mapping of a buried substratum using aeromagnetic and gravity data; application to the southwestern Paris basin

    NASA Astrophysics Data System (ADS)

    Baptiste, Julien; Martelet, Guillaume; Faure, Michel; Beccaletto, Laurent; Chen, Yan; Reninger, Pierre-Alexandre

    2016-04-01

    Mapping the geometries (structure and lithology) of a buried basement is a key for targeting resources and for improving the regional geological knowledge. The Paris basin is a Mesozoic to Cenozoic intraplate basin set up on a Variscan substratum, which crops out in the surrounding massifs. We focus our study on the southwestern part of the Paris basin at its junction with the Aquitaine basin. This Mezo-Cenozoic cover separates the Armorican Massif and the Massif Central which compose of several litho-tectonic units bounded by crustal-scale shear zones. In spite of several lithological and structural correlations between various domains of the two massifs, their geological connection, hidden below the Paris basin sedimentary cover, is still largely debated. Potential field geophysics have proven effective for mapping buried basin/basement interfaces. In order to enhance the cartographic interpretation of these data, we have set up a detailed petrophysical library (field magnetic susceptibility data and density measurements on rock samples) of the Paleozoic rocks outcropping in the Variscan massifs. The combination of aeromagnetic and gravity data supported by the petrophysical signatures and field/borehole geological information, is carried out to propose a new map of the architecture of the Variscan substratum. The new synthetic map of geophysical signature of the Paris basin basement combines: i) the magnetic anomaly reduced to the pole, ii) the vertical gradient of the Bouguer anomaly and iii) the tilt derivative of the magnetic anomaly reduced to the pole. Based on this information, the Eastern extension of the major shear zones below the sedimentary cover is assessed. The petrophysical signatures were classified in three classes of magnetic susceptibility and density: low, intermediate and high. Basic rocks have high magnetization and density values whereas granite, migmatite and orthogneiss show low magnetization and density values, Proterozoic and Paleozoic

  8. On the Gravity of the Hawaiian Islands

    NASA Astrophysics Data System (ADS)

    Flinders, A. F.; Ito, G.; Garcia, M. O.; Taylor, B.

    2011-12-01

    The Hawaiian Islands are part of the most geologically studied intra-plate volcanic island chain. Surprisingly, the only chain wide compilation of marine and terrestrial gravity data is now more than 40 years old. Early terrestrial studies conducted by J. G. Moore, H.L Krivoy, G. P. Woollard, W. E Strange and others in the early 1960's were meant to serve as reconnaissance surveys only. In addition, early marine surveys were limited in both accurate positioning and data density. Detailed analysis of the crustal density structure of the island chain was limited. We present a new chain-wide gravity compilation incorporating the original island-specific survey data, recently published data on the island of Kauai and Hawaii, as well as more than 10 years of newly incorporated marine data collected aboard the University of Hawaii's R/V Kilo Moana. This data was supplemented by surveys aboard the R/V Farnella among others. We present free-air (FAA), simple/complete Bouguer, and residual gravity maps on an unprecedented resolution and geographical extent for the area. This data will be hosted as an interactive Google-Earth overlay at the Hawaii Mapping Research Group (HMRG - www.soest.hawaii.edu/HMRG) and made available to the scientific community. We hope that this dataset will be used for further comparison of the gravity fields of other intra-plate volcanic systems (French Polynesia, etc.) and to constrain seismic studies of crustal structure in the Hawaiian-chain through joint seismic-gravity inversions.

  9. The Effect of Pre-Impact Porosity and Vertical Density Gradients on the Gravity Signature of Lunar Craters as Seen by GRAIL

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, H., IV; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Nimmo, F.; Bierson, C. J.; Phillips, R. J.; Zuber, M. T.

    2015-12-01

    As a result of NASA's dual spacecraft Gravity Recovery And Interior Laboratory (GRAIL) mission [Zuber et al., 2013; doi:10.1126/science.1231507], we now know that the lunar crust is highly porous and that the porosity varies laterally [Wieczorek et al., 2013; doi:10.1126/science.1231530] and vertically [Besserer et al., 2014; doi:10.1002/2014GL060240]. Analysis of complex craters located within the lunar highlands reveals that: 1) craters larger than diameter D~210 have positive Bouguer Anomalies (BAs), 2) craters with D ≲ 100 km have both positive and negative BAs that vary about the (near 0) mean by approximately ± 25 mGal, and, 3) D and BA are anticorrelated for craters with D ≲ 100 km [Soderblom et al., 2015; submitted]. Numerical modeling by Milbury et al. [2015, LPSC] shows that pre-impact porosity is the dominant influence on the gravity signature of complex craters with D ≲ 100 km, and mantle uplift dominates the gravity for those with D > 140 km. Phillips et al. [2015, LPSC] showed that complex craters located in the South Pole-Aitken (SPA) basin tend to have more-negative BAs than similar craters in the highlands. By including (pre-impact) vertical porosity/density gradients in our impact simulations, we reproduce the observed anticorrelation between BA and D for D ≲ 100 km, and the observed difference between the BAs of SPA and highland craters. We use the iSALE hydrocode including pore space compaction [Wünnemann et al., 2006; doi:10.1016/j.icarus.2005.10.013] and dilatant bulking [Collins, 2014; doi:10.1002/2014JE004708] to understand how the gravity signature of impact craters develop. In this study we vary density/porosity with depth. We find that simulations that have constant porosity with depth have a lower BA for a given crater diameter than those with varying porosity. We used two different mean porosities (7% and 14%) and found that the BA increases with increasing porosity, similar to simulations with constant porosity. Larger

  10. Venus gravity

    NASA Technical Reports Server (NTRS)

    Reasenberg, Robert D.

    1993-01-01

    The anomalous gravity field of Venus shows high correlation with surface features revealed by radar. We extract gravity models from the Doppler tracking data from the Pioneer Venus Orbiter (PVO) by means of a two-step process. In the first step, we solve the nonlinear spacecraft state estimation problem using a Kalman filter-smoother. The Kalman filter was evaluated through simulations. This evaluation and some unusual features of the filter are discussed. In the second step, we perform a geophysical inversion using a linear Bayesian estimator. To allow an unbiased comparison between gravity and topography, we use a simulation technique to smooth and distort the radar topographic data so as to yield maps having the same characteristics as our gravity maps. The maps presented cover 2/3 of the surface of Venus and display the strong topography-gravity correlation previously reported. The topography-gravity scatter plots show two distinct trends.

  11. Analysis of spacecraft anomalies

    NASA Technical Reports Server (NTRS)

    Bloomquist, C. E.; Graham, W. C.

    1976-01-01

    The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable.

  12. The mineralogy of global magnetic anomalies

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1984-01-01

    Experimental and analytical data on magnetic mineralogy was provided as an aid to the interpretation of magnetic anomaly maps. An integrated program, ranging from the chemistry of materials from 100 or more km depth within the Earth, to an examination of the MAGSAT anomaly maps at about 400 km above the Earth's surface, was undertaken. Within this framework, a detailed picture of the pertinent mineralogical and magnetic relationships for the region of West Africa was provided. Efforts were directed toward: (1) examining the geochemistry, mineralogy, magnetic properties, and phases relations of magnetic oxides and metal alloys in rocks demonstrated to have originated in the lower crust of upper mantle, (2) examining the assumption that these rocks portray the nature of their source regions; and (3) examining the regional geology, tectonics, gravity field and the MAGSAT anomaly maps for West Africa.

  13. Gravity investigations

    SciTech Connect

    Healey, D.L.

    1983-12-31

    A large density contrast exists between the Paleozoic rocks (including the rocks of Climax stock) and less dense, Tertiary volcanic rocks and alluvium. This density contrast ranges widely, and herein for interpretive purposes, is assumed to average 0.85 Mg/m{sup 3} (megagrams per cubic meter). The large density contrast makes the gravity method a useful tool with which to study the interface between these rock types. However, little or no density contrast is discernible between the sedimentary Paleozoic rocks that surround the Climax stock and the intrusive rocks of the stock itself. Therefore the gravity method can not be used to define the configuration of the stock. Gravity highs coincide with outcrops of the dense Paleozoic rocks, and gravity lows overlie less-dense Tertiary volcanic rocks and Quaternary alluvium. The positions of three major faults (Boundary, Yucca, and Butte faults) are defined by steep gravity gradients. West of the Climax stock, the Tippinip fault has juxtaposed Paleozoic rocks of similar density, and consequently, has no expression in the gravity data in that area. The gravity station spacing, across Oak Spring Butte, is not sufficient to adequately define any gravity expression of the Tippinip fault. 18 refs., 5 figs.

  14. Gravity model studies of Newberry Volcano, Oregon

    SciTech Connect

    Gettings, M.E.; Griscom, A.

    1988-09-10

    Newberry, Volcano, a large Quaternary volcano located about 60 km east of the axis of the High Cascades volcanoes in central Oregon, has a coincident positive residual gravity anomaly of about 12 mGals. Model calculations of the gravity anomaly field suggest that the volcano is underlain by an intrusive complex of mafic composition of about 20-km diameter and 2-km thickness, at depths above 4 km below sea level. However, uplifted basement in a northwest trending ridge may form part of the underlying excess mass, thus reducing the volume of the subvolcanic intrusive. A ring dike of mafic composition is inferred to intrude to near-surface levels along the caldera ring fractures, and low-density fill of the caldera floor probably has a thickness of 0.7--0.9 km. The gravity anomaly attributable to the volcano is reduced to the east across a north-northwest trending gravity anomaly gradient through Newberry caldera and suggests that normal, perhaps extensional, faulting has occurred subsequent to caldera formation and may have controlled the location of some late-stage basaltic and rhyolitic eruptions. Significant amounts of felsic intrusive material may exist above the mafic intrusive zone but cannot be resolved by the gravity data.

  15. Chicxulub impact basin: Gravity characteristics and implications for basin morphology and deep structure

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Burke, Kevin; Hall, Stuart A.; Lee, Scott; Marin, Luis E.; Suarez, Gerardo; Quezada-Muneton, Juan Manuel; Urrutia-Fucugauchi, Jaime

    1993-01-01

    The K-T-aged Chicxulub Impact Structure is buried beneath the Tertiary carbonate rocks of the Northern Yucatan Platform. Consequently its morphology and structure are poorly understood. Reprocessed Bouguer (onshore) and Free Air (offshore) gravity data over Northern Yucatan reveal that Chicxulub may be a 200-km-diameter multi-ring impact basin with at least three concentric basin rings. The positions of these rings follow the square root of 2 spacing rule derived empirically from analysis of multi-ring basins on other planets indicating that these rings probably correspond to now-buried topographic basin rings. A forward model of the gravity data along a radial transect from the southwest margin of the structure indicates that the Chicxulub gravity signature is compatible with this interpretation. We estimate the basin rim diameter to be 204 +/- 16 km and the central peak ring diameter (D) is 104 +/- 6 km.

  16. A deterministic approach toward isostatic gravity residuals: A case study from South America

    SciTech Connect

    Chapin, D.A.

    1994-12-31

    Isostatic gravity residuals are based upon geologic models, therefore they provide a reasonable basis of comparison over large areas for reconnaissance studies. To help define the best isostatic model for South America, a new deterministic methodology overcomes the deficiencies of other empirically-based methods. The basis for the model was the Airy-Heiskanen (1958) isostatic model, which assumes that surface topography is supported by crustal thickening. The three key parameters -- (a) the crustal thickness at sea-level, (b) the surface reduction density, and (c) the density contrast between the crust and the mantle -- were determined directly from the elevation, free-air gravity, and Bouguer gravity datasets. The results of this work were not only an isostatic residual map, but methodology which cross-checks the data for quality control purposes. The final isostatic residual map can be used in confidence for basin evaluation throughout the continent of South America.

  17. [Kimmerle's anomaly and stroke].

    PubMed

    Barsukov, S F; Antonov, G I

    1992-10-01

    The anomaly of cranio-vertebral area can frequently be the reason of acute cerebrovascular disorders in vertebro-basilar field. The frequent C1 pathology in the Kimmerle's anomaly. The anatomic studies has shown that 30% of people had this type of anomaly. This pathology can lead to severe vascular diseases of cerebrum because of the squeezing effect upon vertebral arteries in the zone of osteal ponticulus of the rear arch of atlas. PMID:1481402

  18. Hyperbolic Orbits and the Planetary Flylby Anomaly

    NASA Technical Reports Server (NTRS)

    Wilson, T.L.; Blome, H.J.

    2009-01-01

    Space probes in the Solar System have experienced unexpected changes in velocity known as the flyby anomaly [1], as well as shifts in acceleration referred to as the Pioneer anomaly [2-4]. In the case of Earth flybys, ESA s Rosetta spacecraft experienced the flyby effect and NASA s Galileo and NEAR satellites did the same, although MESSENGER did not possibly due to a latitudinal property of gravity assists. Measurements indicate that both anomalies exist, and explanations have varied from the unconventional to suggestions that new physics in the form of dark matter might be the cause of both [5]. Although dark matter has been studied for over 30 years, there is as yet no strong experimental evidence supporting it [6]. The existence of dark matter will certainly have a significant impact upon ideas regarding the origin of the Solar System. Hence, the subject is very relevant to planetary science. We will point out here that one of the fundamental problems in science, including planetary physics, is consistency. Using the well-known virial theorem in astrophysics, it will be shown that present-day concepts of orbital mechanics and cosmology are not consistent for reasons having to do with the flyby anomaly. Therefore, the basic solution regarding the anomalies should begin with addressing the inconsistencies first before introducing new physics.

  19. Taussig-Bing Anomaly

    PubMed Central

    Konstantinov, Igor E.

    2009-01-01

    Taussig-Bing anomaly is a rare congenital heart malformation that was first described in 1949 by Helen B. Taussig (1898–1986) and Richard J. Bing (1909–). Although substantial improvement has since been achieved in surgical results of the repair of the anomaly, management of the Taussig-Bing anomaly remains challenging. A history of the original description of the anomaly, the life stories of the individuals who first described it, and the current outcomes of its surgical management are reviewed herein. PMID:20069085

  20. Geophysical investigations of a geothermal anomaly at Wadi Ghadir, eastern Egypt

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.; Basta, N. Z.; Melek, Y. S.

    1984-01-01

    During regional heat flow studies a geothermal anomaly was discovered approximately 2 km from the Red Sea coast at Wadi Ghadir, in the Red Sea Hills of Eastern Egypt. A temperature gradient of 55 C/km was measured in a 150 m drillhole at this location, indicating a heat flow of approximately 175 mw/sqm, approximately four times the regional background heat flow for Egypt. Gravity and magnetic data were collected along Wadi Ghadir, and combined with offshore gravity data, to investigate the source of the thermal anomaly. Magnetic anomalies in the profile do not coincide with the thermal anomaly, but were observed to correlate with outcrops of basic rocks. Other regional heat flow and gravity data indicate that the transition from continental to oceanic type lithosphere occurs close to the Red Sea margin, and that the regional thermal anomaly is possibly related to the formation of the Red Sea.

  1. Gravity Currents

    NASA Astrophysics Data System (ADS)

    Simpson, John E.

    1997-03-01

    This book comprehensively describes all aspects of gravity flow, a physical process in the environment that is covered by many disciplines including meteorology, oceanography, the earth sciences and industrial processes. The first edition was very well received, and the author has brought the new edition completely up to date, with much new material. Simpson describes gravity currents with a variety of laboratory experiments, many from his own work. Gravity Currents is a valuable supplementary textbook for undergraduates and a reference work for research workers. The general reader will also find much of interest, since the author clearly describes the physics of flows involved without advanced mathematics, and with numerous photographs and illustrations.

  2. Gravity Currents

    NASA Astrophysics Data System (ADS)

    Simpson, John E.

    1999-11-01

    This book comprehensively describes all aspects of gravity flow, a physical process in the environment that is covered by many disciplines including meteorology, oceanography, the earth sciences and industrial processes. The first edition was very well received, and the author has brought the new edition completely up to date, with much new material. Simpson describes gravity currents with a variety of laboratory experiments, many from his own work. Gravity Currents is a valuable supplementary textbook for undergraduates and a reference work for research workers. The general reader will also find much of interest, since the author clearly describes the physics of flows involved without advanced mathematics, and with numerous photographs and illustrations.

  3. Does the Madden-Julian Oscillation Modulate Stratospheric Gravity Waves?

    NASA Astrophysics Data System (ADS)

    Moss, Andrew; Wright, Corwin; Mitchell, Nicholas

    2016-04-01

    The circulation of the stratosphere is strongly influenced by the fluxes of gravity waves propagating from tropospheric sources. In the tropics, these gravity waves are primarily generated by convection. The Madden-Julian Oscillation (MJO) dominates the intra-seasonal variability of this convection. However, the connection between the MJO and the variability of stratospheric gravity waves is largely unknown. Here we examine gravity-wave potential energy at a height of 26 km and the upper tropospheric zonal-wind anomaly of the MJO at the 200 hPa level, sorted by the relative phase of the MJO using the RMM MJO indices. We show that a strong anti-correlation exists between gravity-wave potential energy and the MJO eastward wind anomaly. We propose that this correlation is a result of the filtering of ascending waves by the MJO winds. The study provides evidence that the MJO contributes significantly to the variability of stratospheric gravity waves in the tropics.

  4. Does the Madden-Julian Oscillation modulate stratospheric gravity waves?

    NASA Astrophysics Data System (ADS)

    Moss, Andrew C.; Wright, Corwin J.; Mitchell, Nicholas J.

    2016-04-01

    The circulation of the stratosphere is strongly influenced by the fluxes of gravity waves propagating from tropospheric sources. In the tropics, these gravity waves are primarily generated by convection. The Madden-Julian Oscillation (MJO) dominates the intraseasonal variability of this convection. However, the influence of the MJO on the variability of stratospheric gravity waves is largely unknown. Here we examine gravity wave potential energy at 26 km and the upper tropospheric zonal wind anomaly of the MJO at 200 hPa, sorted by the relative phase of the MJO using the Real Multivariate MJO indices. We show that a strong anticorrelation exists between gravity wave potential energy and the MJO eastward wind anomaly. We propose that this correlation is a result of the filtering of upward propagating waves by the MJO winds. The study provides the first observational evidence that the MJO contributes significantly to the global variability of stratospheric gravity waves in the tropics.

  5. Gravity brake

    DOEpatents

    Lujan, Richard E.

    2001-01-01

    A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.

  6. Competing Orders and Anomalies.

    PubMed

    Moon, Eun-Gook

    2016-01-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation "laws" could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the 't Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed. PMID:27499184

  7. Competing Orders and Anomalies

    NASA Astrophysics Data System (ADS)

    Moon, Eun-Gook

    2016-08-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation “laws” could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the ’t Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed.

  8. Competing Orders and Anomalies

    PubMed Central

    Moon, Eun-Gook

    2016-01-01

    A conservation law is one of the most fundamental properties in nature, but a certain class of conservation “laws” could be spoiled by intrinsic quantum mechanical effects, so-called quantum anomalies. Profound properties of the anomalies have deepened our understanding in quantum many body systems. Here, we investigate quantum anomaly effects in quantum phase transitions between competing orders and striking consequences of their presence. We explicitly calculate topological nature of anomalies of non-linear sigma models (NLSMs) with the Wess-Zumino-Witten (WZW) terms. The non-perturbative nature is directly related with the ’t Hooft anomaly matching condition: anomalies are conserved in renormalization group flow. By applying the matching condition, we show massless excitations are enforced by the anomalies in a whole phase diagram in sharp contrast to the case of the Landau-Ginzburg-Wilson theory which only has massive excitations in symmetric phases. Furthermore, we find non-perturbative criteria to characterize quantum phase transitions between competing orders. For example, in 4D, we show the two competing order parameter theories, CP(1) and the NLSM with WZW, describe different universality class. Physical realizations and experimental implication of the anomalies are also discussed. PMID:27499184

  9. Geological Features and Crustal Structure of the Cretaceous Middle Benue Trough, Nigeria: Insights from Detailed Analysis and Modelling of Magnetic and Gravity Data

    NASA Astrophysics Data System (ADS)

    Anudu, G. K.; Stephenson, R.; Macdonald, D.

    2015-12-01

    The middle Benue Trough is the middle (central) segment of the Nigerian Benue Trough, an intra-continental rift that developed during the second phase of rifting of the Gondwana supercontinent that resulted in the opening of the South Atlantic Ocean, Gulf of Guinea and separation of South America from Africa in the Late Jurassic to Early Cretaceous. Airborne magnetic and terrestrial gravity data from the area have been analysed and modelled in detail. Results obtained using a variety of edge enhancement (derivative) methods applied to high-resolution, airborne magnetic data reveal widespread magmatic intrusions (mainly volcanic/sub-volcanic rocks, with an areal extent greater than 12000 km2) and numerous geological structures. Rose (azimuth frequency) plots show that the geological structural trends are predominantly NE - SW, NW - SE and ESE - WNW with minor ENE -WSW/N - S trends and thus suggest that the area has undergone several phases of tectonic deformation at different geological times. Integrated two-dimensional (2-D) gravity and magnetic modelling along five profiles constrained by 2-D magnetic depth-to-source estimates and available seismological velocity models indicates the presence of a number of distinct crustal bodies and thin crust. Moho depth varies from ca. 21 - 29 km, while the crustal thickness ranges between ca. 19 and 29 km. Shallower Moho and thinner crust are observed along the trough axis. Results from the study also reveal that the amount of crustal thinning and crustal stretching factor (β) across the area varies from 3.3 - 14.5 km and 1.11 - 1.78, respectively. Broad positive to near positive Bouguer gravity anomalies in the region of the trough axis are due to the combined effects of dense (intermediate to basic) magmatic intrusions (both intra-sedimentary and intra-basement/crustal ones), shallow basement horsts (basement uplift zones) and thin crust replaced by dense abnormal upper mantle bodies. Reactivated intra-basement structures

  10. GRAIL Gravity Observations of Lunar Volcanic Complexes

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.; Zuber, M. T.; McGovern, P. J.; Head, J. W.

    2012-12-01

    Gravity observations by NASA's GRAIL mission are providing important new insights into the volcanic plumbing associated with major volcanic complexes on the Moon. The Marius Hills are the Moon's largest volcanic dome field, consisting of more than 250 basaltic domes and cones and 20 sinuous rilles. There are two distinct free-air gravity anomalies, with the larger anomaly (260 mGal) occurring close to the maximum concentration of volcanic domes in the northern part of the field. Much of the gravity anomaly in this area is due to buried, high density material, mapping out a sill complex with a spatial scale of 200 by 250 kilometers. For plausible choices of density contrast, the sill is more than 2 km thick in the north and 4 km thick in the south. The Aristarchus Plateau is the source for the Moon's largest pyroclastic eruption and numerous sinuous rilles. Most of the gravity anomaly on the plateau itself has relatively low amplitude (< 60 mGal) and is likely due to isostatic or flexurally supported topography. There is a significant gravity high (160 mGal) associated with the Cobra Head, which is the source region for Vallis Schröteri, the largest rille in the Aristarchus Plateau. Regions of high free-air gravity also occur in the plains wrapping around the south and east sides of the plateau and in the adjacent Harbinger Mountains/Prinz Crater volcanic field (150 mGal). These gravity highs are all likely due to buried, high density material, plausibly in the form of volcanic intrusions. The Cauchy volcanic dome complex in eastern Mare Tranquillitatis is a regional topographic high about 400 km across but a free-air gravity low (-90 mGal). Similarly, the Hortensius/Tobias Mayer volcanic field in Mare Insularum is also a free-air gravity low (-80 mGal) in its center. In both cases, this implies the presence of low density material at depth, possibly due to thicker than normal crust. The Rümker Hills in northern Oceanus Procellarum is a small basaltic dome complex

  11. Gravity field determination and error assessment techniques

    NASA Technical Reports Server (NTRS)

    Yuan, D. N.; Shum, C. K.; Tapley, B. D.

    1989-01-01

    Linear estimation theory, along with a new technique to compute relative data weights, was applied to the determination of the Earth's geopotential field and other geophysical model parameters using a combination of satellite ground-based tracking data, satellite altimetry data, and the surface gravimetry data. The relative data weights for the inhomogeneous data sets are estimated simultaneously with the gravity field and other geophysical and orbit parameters in a least squares approach to produce the University of Texas gravity field models. New techniques to perform calibration of the formal covariance matrix for the geopotential solution were developed to obtain a reliable gravity field error estimate. Different techniques, which include orbit residual analysis, surface gravity anomaly residual analysis, subset gravity solution comparisons and consider covariance analysis, were applied to investigate the reliability of the calibration.

  12. Evaluation of recent Earth's global gravity field models with terrestrial gravity data

    NASA Astrophysics Data System (ADS)

    Karpik, Alexander P.; Kanushin, Vadim F.; Ganagina, Irina G.; Goldobin, Denis N.; Kosarev, Nikolay S.; Kosareva, Alexandra M.

    2016-03-01

    In the context of the rapid development of environmental research technologies and techniques to solve scientific and practical problems in different fields of knowledge including geosciences, the study of Earth's gravity field models is still important today. The results of gravity anomaly modelling calculated by the current geopotential models data were compared with the independent terrestrial gravity data for the two territories located in West Siberia and Kazakhstan. Statistical characteristics of comparison results for the models under study were obtained. The results of investigations show that about 70% of the differences between the gravity anomaly values calculated by recent global geopotential models and those observed at the points in flat areas are within ±10 mGal, in mountainous areas are within ±20 mGal.

  13. Müllerian anomalies.

    PubMed

    Gell, Jennifer S

    2003-11-01

    The reproductive organs in both males and females consist of gonads, internal ductal structures, and external genitalia. Normal sexual differentiation is dependent on the genetic sex determined by the presence or absence of the Y chromosome at fertilization. Testes develop under the influence of the Y chromosome and ovaries develop when no Y chromosome is present. In the absence of testes and their normal hormonal products, sexual differentiation proceeds along the female pathway, resulting in a normal female phenotype. Anatomic gynecologic anomalies occur when there is failure of normal embryologic ductal development. These anomalies include congenital absence of the vagina as well as defects in lateral and vertical fusion of the Müllerian ducts. Treatment of müllerian anomalies begins with the correct identification of the anomaly and an understanding of the embryologic origin. This includes evaluation for other associated anomalies such as renal or skeletal abnormalities. After correct identification, treatment options include nonsurgical as well as surgical intervention. This chapter serves to review the embryology and development of the reproductive system and to describe common genital tract anomalies. Details of surgical or nonsurgical correction of these anomalies are presented. PMID:14724770

  14. Behavioral economics without anomalies.

    PubMed Central

    Rachlin, H

    1995-01-01

    Behavioral economics is often conceived as the study of anomalies superimposed on a rational system. As research has progressed, anomalies have multiplied until little is left of rationality. Another conception of behavioral economics is based on the axiom that value is always maximized. It incorporates so-called anomalies either as conflicts between temporal patterns of behavior and the individual acts comprising those patterns or as outcomes of nonexponential time discounting. This second conception of behavioral economics is both empirically based and internally consistent. PMID:8551195

  15. Holographic trace anomaly and local renormalization group

    NASA Astrophysics Data System (ADS)

    Rajagopal, Srivatsan; Stergiou, Andreas; Zhu, Yechao

    2015-11-01

    The Hamilton-Jacobi method in holography has produced important results both at a renormalization group (RG) fixed point and away from it. In this paper we use the Hamilton-Jacobi method to compute the holographic trace anomaly for four- and six-dimensional boundary conformal field theories (CFTs), assuming higher-derivative gravity and interactions of scalar fields in the bulk. The scalar field contributions to the anomaly appear in CFTs with exactly marginal operators. Moving away from the fixed point, we show that the Hamilton-Jacobi formalism provides a deep connection between the holographic and the local RG. We derive the local RG equation holographically, and verify explicitly that it satisfies Weyl consistency conditions stemming from the commutativity of Weyl scalings. We also consider massive scalar fields in the bulk corresponding to boundary relevant operators, and comment on their effects to the local RG equation.

  16. Examination of consistency of marine gravity with land gravity in and around the Japanese Islands using a helicopter-borne gravimeter

    NASA Astrophysics Data System (ADS)

    Segawa, Jiro; Komazawa, Masao; Kumar, K. Vijay; Nakayama, Eiji; Joseph, E. John; Kusumoto, Shigekazu; Onodera, Ken-ei; Kuroishi, Yuki

    2005-04-01

    This paper reports a finding that marine gravity data around the Japanese Islands are inconsistent with nearby land gravity data. The comparison between land and marine gravity was made possible by the gravity measurements from the air using a helicopter-borne gravimeter (SEGAWA Model) developed by the present authors. The ground/sea truth gravity anomaly can be checked against the gravity from the air, though it is not free air gravity anomaly but gravity disturbance. The newly-developed airborne gravimeter first manufactured in 1998 shows a good performance with a 1-2 mgal average repeatability of measurement under a 90-knot flight speed. Thus we have found disagreements between ground truth and sea truth gravity anomalies on the basis of airborne gravity data in the areas in Japan where we have so far made measurements. Among them we will report the case in the area from Saitama and Ibaraki offshore to the Kashima-Nada Sea, p]Japan. Our conclusion about this area is that the past marine gravity data obtained by surface ship gravimeters involve systematic errors of more than 10 mgals. This kind of inconsistency between marine and land gravity is expected to be found in a number of other areas around the Japanese Islands.

  17. Dual diaphragmatic anomalies.

    PubMed

    Padmanabhan, Arjun; Thomas, Abin Varghese

    2016-01-01

    Although diaphragmatic anomalies such as an eventration and hiatus hernia are commonly encountered in incidental chest X-ray imaging, the presence of concomitant multiple anomalies is extremely rare. This is all the more true in adults. Herein, we present the case of a 75-year-old female, while undergoing a routine chest X-ray imaging, was found to have eventration of right hemidiaphragm along with a hiatus hernia as well. PMID:27625457

  18. Dual diaphragmatic anomalies

    PubMed Central

    Padmanabhan, Arjun; Thomas, Abin Varghese

    2016-01-01

    Although diaphragmatic anomalies such as an eventration and hiatus hernia are commonly encountered in incidental chest X-ray imaging, the presence of concomitant multiple anomalies is extremely rare. This is all the more true in adults. Herein, we present the case of a 75-year-old female, while undergoing a routine chest X-ray imaging, was found to have eventration of right hemidiaphragm along with a hiatus hernia as well.

  19. Anomalies and entanglement entropy

    NASA Astrophysics Data System (ADS)

    Nishioka, Tatsuma; Yarom, Amos

    2016-03-01

    We initiate a systematic study of entanglement and Rényi entropies in the presence of gauge and gravitational anomalies in even-dimensional quantum field theories. We argue that the mixed and gravitational anomalies are sensitive to boosts and obtain a closed form expression for their behavior under such transformations. Explicit constructions exhibiting the dependence of entanglement entropy on boosts is provided for theories on spacetimes with non-trivial magnetic fluxes and (or) non-vanishing Pontryagin classes.

  20. Gravity and magnetic evidence for a granitic intrusion near Wahmonie Site, Nevada Test Site, Nevada

    SciTech Connect

    Ponce, D.A.

    1984-10-10

    Gravity and magnetic data outline a broad anomaly near Wahmonie Site, Nye County, Nevada. A positive 15-mGal gravity anomaly with a steep western gradient and a broad magnetic anomaly coincident with the gravity high characterize the area. Two-dimensional computer models of the gravity data were made using magnetic, seismic, and electric data as independent constraints. The models indicate the presence of a shallow, relatively high density body of 2.65 kg m{sup -3} buried near Wahmonie Site. Aeromagnetic and ground magnetic data also indicate the presence of a large, shallow body. Two smaller local magnetic highs that occur along a magnetic prominence extending northward from the broad anomaly directly correlate to granodiorite outcrops. This indicates that the main anomaly is produced by a large shallow intrusion.

  1. Antarctic Crustal Thickness from Gravity Inversion

    NASA Astrophysics Data System (ADS)

    Vaughan, A. P.; Kusznir, N. J.; Ferraccioli, F.; Jordan, T. A.

    2013-12-01

    Using gravity anomaly inversion, we have produced the first comprehensive regional maps of crustal thickness and oceanic lithosphere distribution for Antarctica and the Southern Ocean. We determine Moho depth, crustal basement thickness, continental lithosphere thinning (1-1/β) and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction. The continental lithosphere thinning distribution, used to define the initial thermal model temperature perturbation is derived from the gravity inversion and uses no a priori isochron information; as a consequence the gravity inversion method provides a prediction of ocean-continent transition location, which is independent of ocean isochron information. The gravity anomaly contribution from ice thickness is included in the gravity inversion, as is the contribution from sediments which assumes a compaction controlled sediment density increase with depth. Data used in the gravity inversion are elevation and bathymetry, free-air gravity anomaly, the most recent Bedmap2 ice thickness and bedrock topography compilation south of 60 degrees south (Fretwell et al., 2013) and relatively sparse constraints on sediment thickness. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica penetrated by narrow continental rifts that feature relatively thinner crust. The East Antarctic Rift System (EARS) is a major Permian to Cretaceous age rift system that appears to extend from the continental margin at the Lambert Rift to the South Pole region, a distance of 2500 km. This is comparable in scale to the well-studied East African rift system. Intermediate crustal thickness with an inferred linear rift fabric is predicted under Coates Land. An extensive region of either thick oceanic crust or highly thinned continental crust is predicted offshore Oates Land and north Victoria Land, and also off West Antarctica

  2. Gravity settling

    DOEpatents

    Davis, Hyman R.; Long, R. H.; Simone, A. A.

    1979-01-01

    Solids are separated from a liquid in a gravity settler provided with inclined solid intercepting surfaces to intercept the solid settling path to coalesce the solids and increase the settling rate. The intercepting surfaces are inverted V-shaped plates, each formed from first and second downwardly inclined upwardly curved intersecting conical sections having their apices at the vessel wall.

  3. Simulating Gravity

    ERIC Educational Resources Information Center

    Pipinos, Savas

    2010-01-01

    This article describes one classroom activity in which the author simulates the Newtonian gravity, and employs the Euclidean Geometry with the use of new technologies (NT). The prerequisites for this activity were some knowledge of the formulae for a particle free fall in Physics and most certainly, a good understanding of the notion of similarity…

  4. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Starich, P. J.

    1984-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced to pole and derivative maps provide constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the anomaly, but are rather indicative of a crustal zone which was disturbed during a Middle Proterozoic thermal event which enriched magnetic material deep in the crust.

  5. The south-central United States magnetic anomaly

    NASA Technical Reports Server (NTRS)

    Starich, P. J.

    1985-01-01

    The South-Central United States Magnetic Anomaly is the most prominent positive feature in the MAGSAT scalar magnetic field over North America. The anomaly correlates with increased crustal thickness, above average crustal velocity, negative free-air gravity anomalies and an extensive zone of Middle Proterozoic anorogenic felsic basement rocks. Spherical dipole source inversion of the MAGSAT scalar data and subsequent calculation of reduced-to-pole and derivative maps provide additional constraints for a crustal magnetic model which corresponds geographically to the extensive Middle Proterozoic felsic rocks trending northeasterly across the United States. These felsic rocks contain insufficient magnetization or volume to produce the